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 $84.83   13.173%   $96.0047   $96.00   $96.00   $96.00  
  Purchase #2 $35.91   3.191%   $37.0559   $37.06   $37.05   $37.10  
  Purchase #3 $51.44   5.114%   $54.0706   $54.07   $54.05   $54.10  
  Purchase #4 $118.46   8.308%   $128.3017   $128.30   $128.30   $128.30  
  Purchase #5 $92.82   10.220%   $102.3062   $102.31   $102.30   $102.30  
  Purchase #6 $196.34   5.865%   $207.8553   $207.86   $207.85   $207.90  
  Purchase #7 $98.63   3.605%   $102.1856   $102.19   $102.20   $102.20  
  7 purchase totals = $678.43       $727.7800   $727.79   $727.75   $727.90