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 $32.97   10.381%   $36.3926   $36.39   $36.40   $36.40  
  Purchase #2 $216.48   7.788%   $233.3395   $233.34   $233.35   $233.30  
  Purchase #3 $41.72   5.454%   $43.9954   $44.00   $44.00   $44.00  
  Purchase #4 $240.84   11.387%   $268.2645   $268.26   $268.25   $268.30  
  Purchase #5 $81.87   13.110%   $92.6032   $92.60   $92.60   $92.60  
  Purchase #6 $147.33   3.368%   $152.2921   $152.29   $152.30   $152.30  
  Purchase #7 $215.37   12.382%   $242.0371   $242.04   $242.05   $242.00  
  7 purchase totals = $976.58       $1,068.9244   $1,068.92   $1,068.95   $1,068.90