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 $168.71   12.732%   $190.1902   $190.19   $190.20   $190.20  
  Purchase #2 $116.92   13.685%   $132.9205   $132.92   $132.90   $132.90  
  Purchase #3 $57.64   8.762%   $62.6904   $62.69   $62.70   $62.70  
  Purchase #4 $178.68   11.561%   $199.3372   $199.34   $199.35   $199.30  
  Purchase #5 $137.88   13.128%   $155.9809   $155.98   $156.00   $156.00  
  Purchase #6 $162.31   6.605%   $173.0306   $173.03   $173.05   $173.00  
  Purchase #7 $129.55   7.322%   $139.0357   $139.04   $139.05   $139.00  
  7 purchase totals = $951.69       $1,053.1855   $1,053.19   $1,053.25   $1,053.10