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 $232.28   13.236%   $263.0246   $263.02   $263.00   $263.00  
  Purchase #2 $106.80   9.147%   $116.569   $116.57   $116.55   $116.60  
  Purchase #3 $126.28   8.745%   $137.3232   $137.32   $137.30   $137.30  
  Purchase #4 $83.61   13.570%   $94.9559   $94.96   $94.95   $95.00  
  Purchase #5 $88.42   10.489%   $97.6944   $97.69   $97.70   $97.70  
  Purchase #6 $87.67   10.130%   $96.551   $96.55   $96.55   $96.60  
  Purchase #7 $73.56   7.174%   $78.8372   $78.84   $78.85   $78.80  
  7 purchase totals = $798.62       $884.9553   $884.95   $884.90   $885.00