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 $37.63   13.214%   $42.6024   $42.60   $42.60   $42.60  
  Purchase #2 $59.85   11.123%   $66.5071   $66.51   $66.50   $66.50  
  Purchase #3 $118.42   5.551%   $124.9935   $124.99   $125.00   $125.00  
  Purchase #4 $45.43   3.477%   $47.0096   $47.01   $47.00   $47.00  
  Purchase #5 $84.76   7.761%   $91.3382   $91.34   $91.35   $91.30  
  Purchase #6 $86.96   5.297%   $91.5663   $91.57   $91.55   $91.60  
  Purchase #7 $131.51   6.711%   $140.3356   $140.34   $140.35   $140.30  
  7 purchase totals = $564.56       $604.3527   $604.36   $604.35   $604.30