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 $238.73   10.687%   $264.2431   $264.24   $264.25   $264.20  
  Purchase #2 $200.46   13.534%   $227.5903   $227.59   $227.60   $227.60  
  Purchase #3 $32.57   12.335%   $36.5875   $36.59   $36.60   $36.60  
  Purchase #4 $210.87   10.530%   $233.0746   $233.07   $233.05   $233.10  
  Purchase #5 $182.71   5.736%   $193.1902   $193.19   $193.20   $193.20  
  Purchase #6 $41.57   9.143%   $45.3707   $45.37   $45.35   $45.40  
  Purchase #7 $158.93   10.718%   $175.9641   $175.96   $175.95   $176.00  
  7 purchase totals = $1,065.84       $1,176.0205   $1,176.01   $1,176.00   $1,176.10