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 $164.63   10.259%   $181.5194   $181.52   $181.50   $181.50  
  Purchase #2 $33.49   12.168%   $37.5651   $37.57   $37.55   $37.60  
  Purchase #3 $34.75   6.312%   $36.9434   $36.94   $36.95   $36.90  
  Purchase #4 $223.58   6.129%   $237.2832   $237.28   $237.30   $237.30  
  Purchase #5 $210.36   10.158%   $231.7284   $231.73   $231.75   $231.70  
  Purchase #6 $104.33   3.593%   $108.0786   $108.08   $108.10   $108.10  
  Purchase #7 $164.65   10.106%   $181.2895   $181.29   $181.30   $181.30  
  7 purchase totals = $935.79       $1,014.4076   $1,014.41   $1,014.45   $1,014.40