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 $58.74   8.800%   $63.9091   $63.91   $63.90   $63.90  
  Purchase #2 $183.87   6.781%   $196.3382   $196.34   $196.35   $196.30  
  Purchase #3 $45.53   11.526%   $50.7778   $50.78   $50.80   $50.80  
  Purchase #4 $13.29   8.302%   $14.3933   $14.39   $14.40   $14.40  
  Purchase #5 $212.83   10.605%   $235.4006   $235.40   $235.40   $235.40  
  Purchase #6 $243.75   9.213%   $266.2067   $266.21   $266.20   $266.20  
  Purchase #7 $44.51   6.566%   $47.4325   $47.43   $47.45   $47.40  
  7 purchase totals = $802.52       $874.4582   $874.46   $874.50   $874.40