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 $59.28   13.872%   $67.5033   $67.50   $67.50   $67.50  
  Purchase #2 $21.31   12.370%   $23.946   $23.95   $23.95   $23.90  
  Purchase #3 $161.27   3.874%   $167.5176   $167.52   $167.50   $167.50  
  Purchase #4 $67.52   11.738%   $75.4455   $75.45   $75.45   $75.40  
  Purchase #5 $201.77   7.568%   $217.04   $217.04   $217.05   $217.00  
  Purchase #6 $68.45   4.394%   $71.4577   $71.46   $71.45   $71.50  
  Purchase #7 $91.68   3.398%   $94.7953   $94.80   $94.80   $94.80  
  7 purchase totals = $671.28       $717.7054   $717.72   $717.70   $717.60