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 $245.98   8.581%   $267.0875   $267.09   $267.10   $267.10  
  Purchase #2 $241.70   9.682%   $265.1014   $265.10   $265.10   $265.10  
  Purchase #3 $80.98   3.461%   $83.7827   $83.78   $83.80   $83.80  
  Purchase #4 $119.47   12.471%   $134.3691   $134.37   $134.35   $134.40  
  Purchase #5 $206.42   5.296%   $217.352   $217.35   $217.35   $217.40  
  Purchase #6 $241.30   3.716%   $250.2667   $250.27   $250.25   $250.30  
  Purchase #7 $201.84   11.198%   $224.442   $224.44   $224.45   $224.40  
  7 purchase totals = $1,337.69       $1,442.4014   $1,442.40   $1,442.40   $1,442.50