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 $53.34   8.361%   $57.7998   $57.80   $57.80   $57.80  
  Purchase #2 $164.62   12.266%   $184.8123   $184.81   $184.80   $184.80  
  Purchase #3 $153.29   13.405%   $173.8385   $173.84   $173.85   $173.80  
  Purchase #4 $48.73   13.643%   $55.3782   $55.38   $55.40   $55.40  
  Purchase #5 $37.91   5.828%   $40.1194   $40.12   $40.10   $40.10  
  Purchase #6 $124.92   8.405%   $135.4195   $135.42   $135.40   $135.40  
  Purchase #7 $32.31   12.276%   $36.2764   $36.28   $36.30   $36.30  
  7 purchase totals = $615.12       $683.6441   $683.65   $683.65   $683.60