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 $234.44   13.846%   $266.9006   $266.90   $266.90   $266.90  
  Purchase #2 $187.32   11.615%   $209.0772   $209.08   $209.10   $209.10  
  Purchase #3 $67.47   10.123%   $74.3   $74.30   $74.30   $74.30  
  Purchase #4 $14.92   13.455%   $16.9275   $16.93   $16.95   $16.90  
  Purchase #5 $160.92   4.574%   $168.2805   $168.28   $168.30   $168.30  
  Purchase #6 $83.74   12.209%   $93.9638   $93.96   $93.95   $94.00  
  Purchase #7 $108.25   4.182%   $112.777   $112.78   $112.80   $112.80  
  7 purchase totals = $857.06       $942.2266   $942.23   $942.30   $942.30