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 $239.82   4.756%   $251.2258   $251.23   $251.25   $251.20  
  Purchase #2 $20.47   10.795%   $22.6797   $22.68   $22.70   $22.70  
  Purchase #3 $87.80   4.783%   $91.9995   $92.00   $92.00   $92.00  
  Purchase #4 $44.73   4.814%   $46.8833   $46.88   $46.90   $46.90  
  Purchase #5 $143.88   5.338%   $151.5603   $151.56   $151.55   $151.60  
  Purchase #6 $227.97   10.607%   $252.1508   $252.15   $252.15   $252.20  
  Purchase #7 $185.60   7.426%   $199.3827   $199.38   $199.40   $199.40  
  7 purchase totals = $950.27       $1,015.8821   $1,015.88   $1,015.95   $1,016.00