Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $244.35   12.613%   $275.1699   $275.17   $275.15   $275.20  
  Purchase #2 $183.82   4.755%   $192.5606   $192.56   $192.55   $192.60  
  Purchase #3 $223.74   5.782%   $236.6766   $236.68   $236.70   $236.70  
  Purchase #4 $245.65   12.529%   $276.4275   $276.43   $276.45   $276.40  
  Purchase #5 $233.45   11.678%   $260.7123   $260.71   $260.70   $260.70  
  Purchase #6 $228.68   4.844%   $239.7573   $239.76   $239.75   $239.80  
  Purchase #7 $209.80   7.299%   $225.1133   $225.11   $225.10   $225.10  
  7 purchase totals = $1,569.49       $1,706.4175   $1,706.42   $1,706.40   $1,706.50