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 $65.76   11.820%   $73.5328   $73.53   $73.55   $73.50  
  Purchase #2 $10.57   10.172%   $11.6452   $11.65   $11.65   $11.60  
  Purchase #3 $249.53   10.524%   $275.7905   $275.79   $275.80   $275.80  
  Purchase #4 $31.97   11.746%   $35.7252   $35.73   $35.75   $35.70  
  Purchase #5 $143.62   7.421%   $154.278   $154.28   $154.30   $154.30  
  Purchase #6 $151.68   10.646%   $167.8279   $167.83   $167.85   $167.80  
  Purchase #7 $150.89   8.874%   $164.28   $164.28   $164.30   $164.30  
  7 purchase totals = $804.02       $883.0796   $883.09   $883.20   $883.00