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 $59.84   11.538%   $66.7443   $66.74   $66.75   $66.70  
  Purchase #2 $203.25   13.493%   $230.6745   $230.67   $230.65   $230.70  
  Purchase #3 $233.81   3.291%   $241.5047   $241.50   $241.50   $241.50  
  Purchase #4 $177.99   5.833%   $188.3722   $188.37   $188.35   $188.40  
  Purchase #5 $41.37   4.169%   $43.0947   $43.09   $43.10   $43.10  
  Purchase #6 $128.27   3.148%   $132.3079   $132.31   $132.30   $132.30  
  Purchase #7 $62.72   5.191%   $65.9758   $65.98   $66.00   $66.00  
  7 purchase totals = $907.25       $968.6741   $968.66   $968.65   $968.70