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 $55.95   10.630%   $61.8975   $61.90   $61.90   $61.90  
  Purchase #2 $89.40   7.718%   $96.2999   $96.30   $96.30   $96.30  
  Purchase #3 $122.34   13.639%   $139.026   $139.03   $139.05   $139.00  
  Purchase #4 $56.85   7.137%   $60.9074   $60.91   $60.90   $60.90  
  Purchase #5 $16.95   4.515%   $17.7153   $17.72   $17.70   $17.70  
  Purchase #6 $158.27   5.387%   $166.796   $166.80   $166.80   $166.80  
  Purchase #7 $244.56   12.306%   $274.6556   $274.66   $274.65   $274.70  
  7 purchase totals = $744.32       $817.2977   $817.32   $817.30   $817.30