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 $61.72   11.704%   $68.9437   $68.94   $68.95   $68.90  
  Purchase #2 $120.73   11.778%   $134.9496   $134.95   $134.95   $134.90  
  Purchase #3 $155.79   3.309%   $160.9451   $160.95   $160.95   $160.90  
  Purchase #4 $140.81   12.181%   $157.9621   $157.96   $157.95   $158.00  
  Purchase #5 $162.61   6.360%   $172.952   $172.95   $172.95   $173.00  
  Purchase #6 $5.74   9.522%   $6.2866   $6.29   $6.30   $6.30  
  Purchase #7 $50.83   9.167%   $55.4896   $55.49   $55.50   $55.50  
  7 purchase totals = $698.23       $757.5287   $757.53   $757.55   $757.50