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 $59.94   7.806%   $64.6189   $64.62   $64.60   $64.60  
  Purchase #2 $13.40   4.206%   $13.9636   $13.96   $13.95   $14.00  
  Purchase #3 $202.39   13.136%   $228.976   $228.98   $229.00   $229.00  
  Purchase #4 $92.81   11.815%   $103.7755   $103.78   $103.80   $103.80  
  Purchase #5 $212.88   10.436%   $235.0962   $235.10   $235.10   $235.10  
  Purchase #6 $119.99   4.555%   $125.4555   $125.46   $125.45   $125.50  
  Purchase #7 $108.45   7.198%   $116.2562   $116.26   $116.25   $116.30  
  7 purchase totals = $809.86       $888.1419   $888.16   $888.15   $888.30