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 $160.87   13.210%   $182.1209   $182.12   $182.10   $182.10  
  Purchase #2 $126.99   4.707%   $132.9674   $132.97   $132.95   $133.00  
  Purchase #3 $16.35   4.540%   $17.0923   $17.09   $17.10   $17.10  
  Purchase #4 $205.79   4.371%   $214.7851   $214.79   $214.80   $214.80  
  Purchase #5 $217.55   3.693%   $225.5841   $225.58   $225.60   $225.60  
  Purchase #6 $178.35   9.826%   $195.8747   $195.87   $195.85   $195.90  
  Purchase #7 $48.33   3.428%   $49.9868   $49.99   $50.00   $50.00  
  7 purchase totals = $954.23       $1,018.4113   $1,018.41   $1,018.40   $1,018.50