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 $83.51   12.516%   $93.9621   $93.96   $93.95   $94.00  
  Purchase #2 $87.28   5.229%   $91.8439   $91.84   $91.85   $91.80  
  Purchase #3 $57.43   7.418%   $61.6902   $61.69   $61.70   $61.70  
  Purchase #4 $135.41   5.302%   $142.5894   $142.59   $142.60   $142.60  
  Purchase #5 $219.74   4.138%   $228.8328   $228.83   $228.85   $228.80  
  Purchase #6 $154.63   9.671%   $169.5843   $169.58   $169.60   $169.60  
  Purchase #7 $184.43   13.699%   $209.6951   $209.70   $209.70   $209.70  
  7 purchase totals = $922.43       $998.1978   $998.19   $998.25   $998.20