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 $68.72   6.812%   $73.4012   $73.40   $73.40   $73.40  
  Purchase #2 $94.29   4.524%   $98.5557   $98.56   $98.55   $98.60  
  Purchase #3 $24.55   9.575%   $26.9007   $26.90   $26.90   $26.90  
  Purchase #4 $65.78   11.450%   $73.3118   $73.31   $73.30   $73.30  
  Purchase #5 $241.80   4.807%   $253.4233   $253.42   $253.40   $253.40  
  Purchase #6 $54.62   12.414%   $61.4005   $61.40   $61.40   $61.40  
  Purchase #7 $244.33   5.416%   $257.5629   $257.56   $257.55   $257.60  
  7 purchase totals = $794.09       $844.5561   $844.55   $844.50   $844.60