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   6.802%   $65.4696   $65.47   $65.45   $65.50  
  Purchase #2 $204.57   11.765%   $228.6377   $228.64   $228.65   $228.60  
  Purchase #3 $237.38   7.627%   $255.485   $255.49   $255.50   $255.50  
  Purchase #4 $7.33   5.671%   $7.7457   $7.75   $7.75   $7.70  
  Purchase #5 $141.38   4.848%   $148.2341   $148.23   $148.25   $148.20  
  Purchase #6 $21.44   7.627%   $23.0752   $23.08   $23.10   $23.10  
  Purchase #7 $43.59   12.368%   $48.9812   $48.98   $49.00   $49.00  
  7 purchase totals = $716.99       $777.6285   $777.64   $777.70   $777.60