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 $64.27   9.440%   $70.3371   $70.34   $70.35   $70.30  
  Purchase #2 $81.97   12.679%   $92.363   $92.36   $92.35   $92.40  
  Purchase #3 $213.98   10.777%   $237.0406   $237.04   $237.05   $237.00  
  Purchase #4 $54.33   13.349%   $61.5825   $61.58   $61.60   $61.60  
  Purchase #5 $87.58   11.872%   $97.9775   $97.98   $98.00   $98.00  
  Purchase #6 $101.88   11.765%   $113.8662   $113.87   $113.85   $113.90  
  Purchase #7 $182.26   9.453%   $199.489   $199.49   $199.50   $199.50  
  7 purchase totals = $786.27       $872.6559   $872.66   $872.70   $872.70