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 $206.87   11.151%   $229.9381   $229.94   $229.95   $229.90  
  Purchase #2 $88.57   5.781%   $93.6902   $93.69   $93.70   $93.70  
  Purchase #3 $116.51   3.105%   $120.1276   $120.13   $120.15   $120.10  
  Purchase #4 $22.42   10.753%   $24.8308   $24.83   $24.85   $24.80  
  Purchase #5 $146.70   4.496%   $153.2956   $153.30   $153.30   $153.30  
  Purchase #6 $192.75   11.543%   $214.9991   $215.00   $215.00   $215.00  
  Purchase #7 $205.49   11.870%   $229.8817   $229.88   $229.90   $229.90  
  7 purchase totals = $979.31       $1,066.7631   $1,066.77   $1,066.85   $1,066.70