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 $68.98   10.476%   $76.2063   $76.21   $76.20   $76.20  
  Purchase #2 $13.30   8.347%   $14.4102   $14.41   $14.40   $14.40  
  Purchase #3 $135.81   12.530%   $152.827   $152.83   $152.85   $152.80  
  Purchase #4 $178.25   9.517%   $195.2141   $195.21   $195.20   $195.20  
  Purchase #5 $55.54   11.604%   $61.9849   $61.98   $62.00   $62.00  
  Purchase #6 $191.88   5.832%   $203.0704   $203.07   $203.05   $203.10  
  Purchase #7 $52.37   8.743%   $56.9487   $56.95   $56.95   $56.90  
  7 purchase totals = $696.13       $760.6616   $760.66   $760.65   $760.60