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 $83.43   4.596%   $87.2644   $87.26   $87.25   $87.30  
  Purchase #2 $188.47   9.302%   $206.0015   $206.00   $206.00   $206.00  
  Purchase #3 $17.57   13.795%   $19.9938   $19.99   $20.00   $20.00  
  Purchase #4 $242.80   3.354%   $250.9435   $250.94   $250.95   $250.90  
  Purchase #5 $204.60   7.277%   $219.4887   $219.49   $219.50   $219.50  
  Purchase #6 $185.93   8.415%   $201.576   $201.58   $201.60   $201.60  
  Purchase #7 $244.72   7.201%   $262.3423   $262.34   $262.35   $262.30  
  7 purchase totals = $1,167.52       $1,247.6102   $1,247.60   $1,247.65   $1,247.60