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 $172.67   12.788%   $194.751   $194.75   $194.75   $194.80  
  Purchase #2 $73.95   5.142%   $77.7525   $77.75   $77.75   $77.80  
  Purchase #3 $40.44   12.207%   $45.3765   $45.38   $45.40   $45.40  
  Purchase #4 $170.50   13.674%   $193.8142   $193.81   $193.80   $193.80  
  Purchase #5 $188.96   9.592%   $207.085   $207.09   $207.10   $207.10  
  Purchase #6 $200.25   8.862%   $217.9962   $218.00   $218.00   $218.00  
  Purchase #7 $34.56   5.762%   $36.5513   $36.55   $36.55   $36.60  
  7 purchase totals = $881.33       $973.3267   $973.33   $973.35   $973.50