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 $51.97   11.510%   $57.9517   $57.95   $57.95   $58.00  
  Purchase #2 $250.39   7.496%   $269.1592   $269.16   $269.15   $269.20  
  Purchase #3 $126.37   3.225%   $130.4454   $130.45   $130.45   $130.40  
  Purchase #4 $92.95   11.594%   $103.7266   $103.73   $103.75   $103.70  
  Purchase #5 $167.84   6.585%   $178.8923   $178.89   $178.90   $178.90  
  Purchase #6 $115.30   12.471%   $129.6791   $129.68   $129.70   $129.70  
  Purchase #7 $157.47   4.531%   $164.605   $164.61   $164.60   $164.60  
  7 purchase totals = $962.29       $1,034.4593   $1,034.47   $1,034.50   $1,034.50