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 $26.47   10.489%   $29.2464   $29.25   $29.25   $29.20  
  Purchase #2 $163.51   6.362%   $173.9125   $173.91   $173.90   $173.90  
  Purchase #3 $44.39   4.128%   $46.2224   $46.22   $46.20   $46.20  
  Purchase #4 $175.53   4.431%   $183.3077   $183.31   $183.30   $183.30  
  Purchase #5 $228.32   8.269%   $247.1998   $247.20   $247.20   $247.20  
  Purchase #6 $162.51   4.195%   $169.3273   $169.33   $169.35   $169.30  
  Purchase #7 $151.42   12.592%   $170.4868   $170.49   $170.50   $170.50  
  7 purchase totals = $952.15       $1,019.7029   $1,019.71   $1,019.70   $1,019.60