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 $194.38   4.311%   $202.7597   $202.76   $202.75   $202.80  
  Purchase #2 $227.86   10.541%   $251.8787   $251.88   $251.90   $251.90  
  Purchase #3 $65.35   13.723%   $74.318   $74.32   $74.30   $74.30  
  Purchase #4 $78.80   13.792%   $89.6681   $89.67   $89.65   $89.70  
  Purchase #5 $57.75   12.439%   $64.9335   $64.93   $64.95   $64.90  
  Purchase #6 $222.87   5.439%   $234.9919   $234.99   $235.00   $235.00  
  Purchase #7 $81.70   4.199%   $85.1306   $85.13   $85.15   $85.10  
  7 purchase totals = $928.71       $1,003.6805   $1,003.68   $1,003.70   $1,003.70