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 $56.94   13.671%   $64.7243   $64.72   $64.70   $64.70  
  Purchase #2 $119.37   13.337%   $135.2904   $135.29   $135.30   $135.30  
  Purchase #3 $84.94   10.660%   $93.9946   $93.99   $94.00   $94.00  
  Purchase #4 $48.28   7.182%   $51.7475   $51.75   $51.75   $51.70  
  Purchase #5 $154.35   8.577%   $167.5886   $167.59   $167.60   $167.60  
  Purchase #6 $58.81   5.124%   $61.8234   $61.82   $61.80   $61.80  
  Purchase #7 $222.53   4.268%   $232.0276   $232.03   $232.05   $232.00  
  7 purchase totals = $745.22       $807.1964   $807.19   $807.20   $807.10