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 $185.82   11.681%   $207.5256   $207.53   $207.55   $207.50  
  Purchase #2 $247.25   8.287%   $267.7396   $267.74   $267.75   $267.70  
  Purchase #3 $167.35   3.839%   $173.7746   $173.77   $173.75   $173.80  
  Purchase #4 $183.49   12.277%   $206.0171   $206.02   $206.00   $206.00  
  Purchase #5 $6.77   9.307%   $7.4001   $7.40   $7.40   $7.40  
  Purchase #6 $215.39   10.704%   $238.4453   $238.45   $238.45   $238.40  
  Purchase #7 $129.98   11.169%   $144.4975   $144.50   $144.50   $144.50  
  7 purchase totals = $1,136.05       $1,245.3998   $1,245.41   $1,245.40   $1,245.30