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 $54.85   12.459%   $61.6838   $61.68   $61.70   $61.70  
  Purchase #2 $51.53   9.427%   $56.3877   $56.39   $56.40   $56.40  
  Purchase #3 $151.98   8.442%   $164.8102   $164.81   $164.80   $164.80  
  Purchase #4 $66.40   4.432%   $69.3428   $69.34   $69.35   $69.30  
  Purchase #5 $139.68   10.321%   $154.0964   $154.10   $154.10   $154.10  
  Purchase #6 $188.61   8.269%   $204.2062   $204.21   $204.20   $204.20  
  Purchase #7 $86.77   6.278%   $92.2174   $92.22   $92.20   $92.20  
  7 purchase totals = $739.82       $802.7445   $802.75   $802.75   $802.70