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 $51.63   12.291%   $57.9758   $57.98   $58.00   $58.00  
  Purchase #2 $73.84   5.232%   $77.7033   $77.70   $77.70   $77.70  
  Purchase #3 $157.65   5.595%   $166.4705   $166.47   $166.45   $166.50  
  Purchase #4 $82.81   12.747%   $93.3658   $93.37   $93.35   $93.40  
  Purchase #5 $236.94   9.710%   $259.9469   $259.95   $259.95   $259.90  
  Purchase #6 $72.39   11.119%   $80.439   $80.44   $80.45   $80.40  
  Purchase #7 $19.62   3.394%   $20.2859   $20.29   $20.30   $20.30  
  7 purchase totals = $694.88       $756.1872   $756.20   $756.20   $756.20