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 $180.41   12.505%   $202.9703   $202.97   $202.95   $203.00  
  Purchase #2 $206.94   10.464%   $228.5942   $228.59   $228.60   $228.60  
  Purchase #3 $245.62   9.161%   $268.1212   $268.12   $268.10   $268.10  
  Purchase #4 $86.29   5.230%   $90.803   $90.80   $90.80   $90.80  
  Purchase #5 $75.61   5.326%   $79.637   $79.64   $79.65   $79.60  
  Purchase #6 $128.47   11.636%   $143.4188   $143.42   $143.40   $143.40  
  Purchase #7 $200.73   8.255%   $217.3003   $217.30   $217.30   $217.30  
  7 purchase totals = $1,124.07       $1,230.8448   $1,230.84   $1,230.80   $1,230.80