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 $64.67   13.397%   $73.3338   $73.33   $73.35   $73.30  
  Purchase #2 $84.46   11.285%   $93.9913   $93.99   $94.00   $94.00  
  Purchase #3 $197.28   7.638%   $212.3482   $212.35   $212.35   $212.30  
  Purchase #4 $38.77   8.700%   $42.143   $42.14   $42.15   $42.10  
  Purchase #5 $58.91   5.454%   $62.123   $62.12   $62.10   $62.10  
  Purchase #6 $224.95   5.339%   $236.9601   $236.96   $236.95   $237.00  
  Purchase #7 $187.60   7.764%   $202.1653   $202.17   $202.15   $202.20  
  7 purchase totals = $856.64       $923.0647   $923.06   $923.05   $923.00