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 $57.31   7.518%   $61.6186   $61.62   $61.60   $61.60  
  Purchase #2 $87.91   11.146%   $97.7084   $97.71   $97.70   $97.70  
  Purchase #3 $20.64   11.289%   $22.97   $22.97   $22.95   $23.00  
  Purchase #4 $52.79   4.354%   $55.0885   $55.09   $55.10   $55.10  
  Purchase #5 $215.66   12.646%   $242.9324   $242.93   $242.95   $242.90  
  Purchase #6 $65.39   12.197%   $73.3656   $73.37   $73.35   $73.40  
  Purchase #7 $127.96   11.234%   $142.335   $142.34   $142.35   $142.30  
  7 purchase totals = $627.66       $696.0185   $696.03   $696.00   $696.00