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 $194.45   8.780%   $211.5227   $211.52   $211.50   $211.50  
  Purchase #2 $160.25   6.606%   $170.8361   $170.84   $170.85   $170.80  
  Purchase #3 $66.84   11.138%   $74.2846   $74.28   $74.30   $74.30  
  Purchase #4 $31.89   9.362%   $34.8755   $34.88   $34.90   $34.90  
  Purchase #5 $162.67   7.749%   $175.2753   $175.28   $175.30   $175.30  
  Purchase #6 $101.42   8.844%   $110.3896   $110.39   $110.40   $110.40  
  Purchase #7 $15.28   11.634%   $17.0577   $17.06   $17.05   $17.10  
  7 purchase totals = $732.80       $794.2415   $794.25   $794.30   $794.30