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 $57.48   4.118%   $59.847   $59.85   $59.85   $59.80  
  Purchase #2 $117.80   10.561%   $130.2409   $130.24   $130.25   $130.20  
  Purchase #3 $146.88   11.303%   $163.4818   $163.48   $163.50   $163.50  
  Purchase #4 $186.95   6.762%   $199.5916   $199.59   $199.60   $199.60  
  Purchase #5 $112.62   5.662%   $118.9965   $119.00   $119.00   $119.00  
  Purchase #6 $40.84   12.282%   $45.856   $45.86   $45.85   $45.90  
  Purchase #7 $135.41   6.590%   $144.3335   $144.33   $144.35   $144.30  
  7 purchase totals = $797.98       $862.3473   $862.35   $862.40   $862.30