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 $228.78   6.635%   $243.9596   $243.96   $243.95   $244.00  
  Purchase #2 $165.40   10.375%   $182.5603   $182.56   $182.55   $182.60  
  Purchase #3 $20.28   5.305%   $21.3559   $21.36   $21.35   $21.40  
  Purchase #4 $86.96   5.269%   $91.5419   $91.54   $91.55   $91.50  
  Purchase #5 $137.87   7.434%   $148.1193   $148.12   $148.10   $148.10  
  Purchase #6 $106.39   3.660%   $110.2839   $110.28   $110.30   $110.30  
  Purchase #7 $239.54   12.266%   $268.922   $268.92   $268.90   $268.90  
  7 purchase totals = $985.22       $1,066.7429   $1,066.74   $1,066.70   $1,066.80