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 $61.30   7.154%   $65.6854   $65.69   $65.70   $65.70  
  Purchase #2 $36.84   4.871%   $38.6345   $38.63   $38.65   $38.60  
  Purchase #3 $187.78   4.114%   $195.5053   $195.51   $195.50   $195.50  
  Purchase #4 $68.54   13.414%   $77.734   $77.73   $77.75   $77.70  
  Purchase #5 $192.90   13.285%   $218.5268   $218.53   $218.55   $218.50  
  Purchase #6 $11.81   5.767%   $12.4911   $12.49   $12.50   $12.50  
  Purchase #7 $38.27   5.433%   $40.3492   $40.35   $40.35   $40.30  
  7 purchase totals = $597.44       $648.9263   $648.93   $649.00   $648.80