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 $60.40   12.633%   $68.0303   $68.03   $68.05   $68.00  
  Purchase #2 $133.98   13.332%   $151.8422   $151.84   $151.85   $151.80  
  Purchase #3 $48.72   13.423%   $55.2597   $55.26   $55.25   $55.30  
  Purchase #4 $67.53   8.349%   $73.1681   $73.17   $73.15   $73.20  
  Purchase #5 $188.47   11.162%   $209.507   $209.51   $209.50   $209.50  
  Purchase #6 $11.75   6.271%   $12.4868   $12.49   $12.50   $12.50  
  Purchase #7 $130.67   5.122%   $137.3629   $137.36   $137.35   $137.40  
  7 purchase totals = $641.52       $707.6570   $707.66   $707.65   $707.70