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 $85.97   11.725%   $96.05   $96.05   $96.05   $96.10  
  Purchase #2 $96.47   7.228%   $103.4429   $103.44   $103.45   $103.40  
  Purchase #3 $48.42   5.735%   $51.1969   $51.20   $51.20   $51.20  
  Purchase #4 $235.29   7.221%   $252.2803   $252.28   $252.30   $252.30  
  Purchase #5 $91.68   11.471%   $102.1966   $102.20   $102.20   $102.20  
  Purchase #6 $75.47   4.511%   $78.8745   $78.87   $78.85   $78.90  
  Purchase #7 $157.74   9.585%   $172.8594   $172.86   $172.85   $172.90  
  7 purchase totals = $791.04       $856.9006   $856.90   $856.90   $857.00