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 $217.81   12.177%   $244.3327   $244.33   $244.35   $244.30  
  Purchase #2 $211.62   6.482%   $225.3372   $225.34   $225.35   $225.30  
  Purchase #3 $44.81   8.612%   $48.669   $48.67   $48.65   $48.70  
  Purchase #4 $135.50   3.276%   $139.939   $139.94   $139.95   $139.90  
  Purchase #5 $100.77   13.397%   $114.2702   $114.27   $114.25   $114.30  
  Purchase #6 $107.34   10.682%   $118.8061   $118.81   $118.80   $118.80  
  Purchase #7 $101.95   8.450%   $110.5648   $110.56   $110.55   $110.60  
  7 purchase totals = $919.80       $1,001.9190   $1,001.92   $1,001.90   $1,001.90