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 $59.48   11.118%   $66.093   $66.09   $66.10   $66.10  
  Purchase #2 $157.39   6.668%   $167.8848   $167.88   $167.90   $167.90  
  Purchase #3 $29.66   10.499%   $32.774   $32.77   $32.75   $32.80  
  Purchase #4 $72.28   5.523%   $76.272   $76.27   $76.25   $76.30  
  Purchase #5 $219.92   10.180%   $242.3079   $242.31   $242.30   $242.30  
  Purchase #6 $216.89   9.575%   $237.6572   $237.66   $237.65   $237.70  
  Purchase #7 $135.95   4.376%   $141.8992   $141.90   $141.90   $141.90  
  7 purchase totals = $891.57       $964.8881   $964.88   $964.85   $965.00