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 $49.67   8.859%   $54.0703   $54.07   $54.05   $54.10  
  Purchase #2 $193.55   4.130%   $201.5436   $201.54   $201.55   $201.50  
  Purchase #3 $64.41   6.222%   $68.4176   $68.42   $68.40   $68.40  
  Purchase #4 $107.93   10.295%   $119.0414   $119.04   $119.05   $119.00  
  Purchase #5 $44.58   13.814%   $50.7383   $50.74   $50.75   $50.70  
  Purchase #6 $93.73   3.420%   $96.9356   $96.94   $96.95   $96.90  
  Purchase #7 $158.56   3.307%   $163.8036   $163.80   $163.80   $163.80  
  7 purchase totals = $712.43       $754.5504   $754.55   $754.55   $754.40