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 $30.46   7.733%   $32.8155   $32.82   $32.80   $32.80  
  Purchase #2 $220.55   3.399%   $228.0465   $228.05   $228.05   $228.00  
  Purchase #3 $219.39   5.725%   $231.9501   $231.95   $231.95   $232.00  
  Purchase #4 $67.52   12.453%   $75.9283   $75.93   $75.95   $75.90  
  Purchase #5 $179.59   13.575%   $203.9693   $203.97   $203.95   $204.00  
  Purchase #6 $161.71   8.238%   $175.0317   $175.03   $175.05   $175.00  
  Purchase #7 $44.92   12.806%   $50.6725   $50.67   $50.65   $50.70  
  7 purchase totals = $924.14       $998.4139   $998.42   $998.40   $998.40