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 $164.89   6.277%   $175.2401   $175.24   $175.25   $175.20  
  Purchase #2 $87.72   11.152%   $97.5025   $97.50   $97.50   $97.50  
  Purchase #3 $130.70   5.608%   $138.0297   $138.03   $138.05   $138.00  
  Purchase #4 $239.49   11.853%   $267.8767   $267.88   $267.90   $267.90  
  Purchase #5 $144.82   4.691%   $151.6135   $151.61   $151.60   $151.60  
  Purchase #6 $133.61   5.424%   $140.857   $140.86   $140.85   $140.90  
  Purchase #7 $185.35   11.321%   $206.3335   $206.33   $206.35   $206.30  
  7 purchase totals = $1,086.58       $1,177.4530   $1,177.45   $1,177.50   $1,177.40