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 $64.32   7.102%   $68.888   $68.89   $68.90   $68.90  
  Purchase #2 $119.71   8.165%   $129.4843   $129.48   $129.50   $129.50  
  Purchase #3 $123.37   11.727%   $137.8376   $137.84   $137.85   $137.80  
  Purchase #4 $61.90   5.459%   $65.2791   $65.28   $65.30   $65.30  
  Purchase #5 $167.84   6.469%   $178.6976   $178.70   $178.70   $178.70  
  Purchase #6 $118.27   3.766%   $122.724   $122.72   $122.70   $122.70  
  Purchase #7 $53.62   11.738%   $59.9139   $59.91   $59.90   $59.90  
  7 purchase totals = $709.03       $762.8245   $762.82   $762.85   $762.80