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 $61.42   9.548%   $67.2844   $67.28   $67.30   $67.30  
  Purchase #2 $245.43   9.355%   $268.39   $268.39   $268.40   $268.40  
  Purchase #3 $55.51   9.348%   $60.6991   $60.70   $60.70   $60.70  
  Purchase #4 $239.36   4.838%   $250.9402   $250.94   $250.95   $250.90  
  Purchase #5 $102.33   11.201%   $113.792   $113.79   $113.80   $113.80  
  Purchase #6 $200.40   8.571%   $217.5763   $217.58   $217.60   $217.60  
  Purchase #7 $45.45   13.294%   $51.4921   $51.49   $51.50   $51.50  
  7 purchase totals = $949.90       $1,030.1741   $1,030.17   $1,030.25   $1,030.20