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 $61.41   12.383%   $69.0144   $69.01   $69.00   $69.00  
  Purchase #2 $86.81   6.152%   $92.1506   $92.15   $92.15   $92.20  
  Purchase #3 $170.87   12.685%   $192.5449   $192.54   $192.55   $192.50  
  Purchase #4 $223.39   10.203%   $246.1825   $246.18   $246.20   $246.20  
  Purchase #5 $146.71   13.162%   $166.02   $166.02   $166.00   $166.00  
  Purchase #6 $169.66   5.169%   $178.4297   $178.43   $178.45   $178.40  
  Purchase #7 $23.39   10.686%   $25.8895   $25.89   $25.90   $25.90  
  7 purchase totals = $882.24       $970.2316   $970.22   $970.25   $970.20