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 $187.54   8.419%   $203.329   $203.33   $203.35   $203.30  
  Purchase #2 $247.49   11.845%   $276.8052   $276.81   $276.80   $276.80  
  Purchase #3 $66.96   13.491%   $75.9936   $75.99   $76.00   $76.00  
  Purchase #4 $49.48   12.846%   $55.8362   $55.84   $55.85   $55.80  
  Purchase #5 $154.77   5.210%   $162.8335   $162.83   $162.85   $162.80  
  Purchase #6 $71.80   3.360%   $74.2125   $74.21   $74.20   $74.20  
  Purchase #7 $108.94   10.121%   $119.9658   $119.97   $119.95   $120.00  
  7 purchase totals = $886.98       $968.9758   $968.98   $969.00   $968.90