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 $46.79   3.189%   $48.2821   $48.28   $48.30   $48.30  
  Purchase #2 $91.88   5.144%   $96.6063   $96.61   $96.60   $96.60  
  Purchase #3 $113.26   5.412%   $119.3896   $119.39   $119.40   $119.40  
  Purchase #4 $55.46   9.563%   $60.7636   $60.76   $60.75   $60.80  
  Purchase #5 $242.59   10.258%   $267.4749   $267.47   $267.45   $267.50  
  Purchase #6 $200.75   11.377%   $223.5893   $223.59   $223.60   $223.60  
  Purchase #7 $8.37   10.629%   $9.2596   $9.26   $9.25   $9.30  
  7 purchase totals = $759.10       $825.3654   $825.36   $825.35   $825.50