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 $56.48   12.589%   $63.5903   $63.59   $63.60   $63.60  
  Purchase #2 $134.92   4.511%   $141.0062   $141.01   $141.00   $141.00  
  Purchase #3 $207.63   13.341%   $235.3299   $235.33   $235.35   $235.30  
  Purchase #4 $227.41   7.548%   $244.5749   $244.57   $244.55   $244.60  
  Purchase #5 $232.73   12.827%   $262.5823   $262.58   $262.60   $262.60  
  Purchase #6 $146.50   3.259%   $151.2744   $151.27   $151.25   $151.30  
  Purchase #7 $187.34   12.121%   $210.0475   $210.05   $210.05   $210.00  
  7 purchase totals = $1,193.01       $1,308.4055   $1,308.40   $1,308.40   $1,308.40