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 $162.97   12.454%   $183.2663   $183.27   $183.25   $183.30  
  Purchase #2 $65.88   13.801%   $74.9721   $74.97   $74.95   $75.00  
  Purchase #3 $190.28   12.476%   $214.0193   $214.02   $214.00   $214.00  
  Purchase #4 $21.36   11.535%   $23.8239   $23.82   $23.80   $23.80  
  Purchase #5 $155.50   11.482%   $173.3545   $173.35   $173.35   $173.40  
  Purchase #6 $236.27   7.202%   $253.2862   $253.29   $253.30   $253.30  
  Purchase #7 $84.89   9.274%   $92.7627   $92.76   $92.75   $92.80  
  7 purchase totals = $917.15       $1,015.4850   $1,015.48   $1,015.40   $1,015.60