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 $20.77   3.687%   $21.5358   $21.54   $21.55   $21.50  
  Purchase #2 $225.63   12.454%   $253.73   $253.73   $253.75   $253.70  
  Purchase #3 $245.73   3.134%   $253.4312   $253.43   $253.45   $253.40  
  Purchase #4 $109.89   10.405%   $121.3241   $121.32   $121.30   $121.30  
  Purchase #5 $147.86   5.567%   $156.0914   $156.09   $156.10   $156.10  
  Purchase #6 $94.70   13.643%   $107.6199   $107.62   $107.60   $107.60  
  Purchase #7 $164.64   3.759%   $170.8288   $170.83   $170.85   $170.80  
  7 purchase totals = $1,009.22       $1,084.5612   $1,084.56   $1,084.60   $1,084.40