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 $120.86   3.874%   $125.5421   $125.54   $125.55   $125.50  
  Purchase #2 $66.33   11.660%   $74.0641   $74.06   $74.05   $74.10  
  Purchase #3 $198.82   3.232%   $205.2459   $205.25   $205.25   $205.20  
  Purchase #4 $236.73   3.326%   $244.6036   $244.60   $244.60   $244.60  
  Purchase #5 $211.45   12.540%   $237.9658   $237.97   $237.95   $238.00  
  Purchase #6 $88.32   4.803%   $92.562   $92.56   $92.55   $92.60  
  Purchase #7 $241.32   6.609%   $257.2688   $257.27   $257.25   $257.30  
  7 purchase totals = $1,163.83       $1,237.2523   $1,237.25   $1,237.20   $1,237.30