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 $240.66   10.242%   $265.3084   $265.31   $265.30   $265.30  
  Purchase #2 $164.55   12.119%   $184.4918   $184.49   $184.50   $184.50  
  Purchase #3 $33.45   8.826%   $36.4023   $36.40   $36.40   $36.40  
  Purchase #4 $98.84   5.515%   $104.291   $104.29   $104.30   $104.30  
  Purchase #5 $187.88   9.312%   $205.3754   $205.38   $205.40   $205.40  
  Purchase #6 $106.27   9.668%   $116.5442   $116.54   $116.55   $116.50  
  Purchase #7 $127.96   6.567%   $136.3631   $136.36   $136.35   $136.40  
  7 purchase totals = $959.61       $1,048.7762   $1,048.77   $1,048.80   $1,048.80