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 $133.91   13.267%   $151.6758   $151.68   $151.70   $151.70  
  Purchase #2 $214.34   8.350%   $232.2374   $232.24   $232.25   $232.20  
  Purchase #3 $116.95   10.184%   $128.8602   $128.86   $128.85   $128.90  
  Purchase #4 $14.75   9.723%   $16.1841   $16.18   $16.20   $16.20  
  Purchase #5 $197.67   4.349%   $206.2667   $206.27   $206.25   $206.30  
  Purchase #6 $132.30   9.431%   $144.7772   $144.78   $144.80   $144.80  
  Purchase #7 $154.89   7.199%   $166.0405   $166.04   $166.05   $166.00  
  7 purchase totals = $964.81       $1,046.0419   $1,046.05   $1,046.10   $1,046.10