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 $182.74   13.402%   $207.2308   $207.23   $207.25   $207.20  
  Purchase #2 $190.81   4.144%   $198.7172   $198.72   $198.70   $198.70  
  Purchase #3 $166.50   7.469%   $178.9359   $178.94   $178.95   $178.90  
  Purchase #4 $43.86   10.814%   $48.603   $48.60   $48.60   $48.60  
  Purchase #5 $99.92   4.344%   $104.2605   $104.26   $104.25   $104.30  
  Purchase #6 $91.72   7.544%   $98.6394   $98.64   $98.65   $98.60  
  Purchase #7 $61.79   6.204%   $65.6235   $65.62   $65.60   $65.60  
  7 purchase totals = $837.34       $902.0103   $902.01   $902.00   $901.90