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 $23.50   8.797%   $25.5673   $25.57   $25.55   $25.60  
  Purchase #2 $232.36   3.811%   $241.2152   $241.22   $241.20   $241.20  
  Purchase #3 $54.31   6.108%   $57.6273   $57.63   $57.65   $57.60  
  Purchase #4 $88.71   4.745%   $92.9193   $92.92   $92.90   $92.90  
  Purchase #5 $170.80   5.589%   $180.346   $180.35   $180.35   $180.30  
  Purchase #6 $158.33   3.555%   $163.9586   $163.96   $163.95   $164.00  
  Purchase #7 $46.83   4.644%   $49.0048   $49.00   $49.00   $49.00  
  7 purchase totals = $774.84       $810.6385   $810.65   $810.60   $810.60