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 $56.25   3.578%   $58.2626   $58.26   $58.25   $58.30  
  Purchase #2 $87.34   9.361%   $95.5159   $95.52   $95.50   $95.50  
  Purchase #3 $67.52   6.176%   $71.69   $71.69   $71.70   $71.70  
  Purchase #4 $118.65   11.561%   $132.3671   $132.37   $132.35   $132.40  
  Purchase #5 $205.94   4.229%   $214.6492   $214.65   $214.65   $214.60  
  Purchase #6 $131.99   13.331%   $149.5856   $149.59   $149.60   $149.60  
  Purchase #7 $16.50   9.749%   $18.1086   $18.11   $18.10   $18.10  
  7 purchase totals = $684.19       $740.1790   $740.19   $740.15   $740.20