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 $93.54   4.322%   $97.5828   $97.58   $97.60   $97.60  
  Purchase #2 $185.85   4.208%   $193.6706   $193.67   $193.65   $193.70  
  Purchase #3 $180.53   11.344%   $201.0093   $201.01   $201.00   $201.00  
  Purchase #4 $209.96   5.185%   $220.8464   $220.85   $220.85   $220.80  
  Purchase #5 $60.31   7.326%   $64.7283   $64.73   $64.75   $64.70  
  Purchase #6 $148.83   4.389%   $155.3621   $155.36   $155.35   $155.40  
  Purchase #7 $38.56   5.410%   $40.6461   $40.65   $40.65   $40.60  
  7 purchase totals = $917.58       $973.8456   $973.85   $973.85   $973.80