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 $180.95   5.751%   $191.3564   $191.36   $191.35   $191.40  
  Purchase #2 $29.54   10.654%   $32.6872   $32.69   $32.70   $32.70  
  Purchase #3 $159.39   5.716%   $168.5007   $168.50   $168.50   $168.50  
  Purchase #4 $127.49   7.355%   $136.8669   $136.87   $136.85   $136.90  
  Purchase #5 $206.32   11.104%   $229.2298   $229.23   $229.25   $229.20  
  Purchase #6 $116.81   10.691%   $129.2982   $129.30   $129.30   $129.30  
  Purchase #7 $61.65   9.179%   $67.3089   $67.31   $67.30   $67.30  
  7 purchase totals = $882.15       $955.2481   $955.26   $955.25   $955.30