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 $202.85   11.684%   $226.551   $226.55   $226.55   $226.60  
  Purchase #2 $246.49   10.317%   $271.9204   $271.92   $271.90   $271.90  
  Purchase #3 $161.95   9.145%   $176.7603   $176.76   $176.75   $176.80  
  Purchase #4 $69.99   9.742%   $76.8084   $76.81   $76.80   $76.80  
  Purchase #5 $106.63   5.734%   $112.7442   $112.74   $112.75   $112.70  
  Purchase #6 $84.55   9.179%   $92.3108   $92.31   $92.30   $92.30  
  Purchase #7 $72.98   8.286%   $79.0271   $79.03   $79.05   $79.00  
  7 purchase totals = $945.44       $1,036.1222   $1,036.12   $1,036.10   $1,036.10