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 $206.86   13.111%   $233.9814   $233.98   $234.00   $234.00  
  Purchase #2 $192.32   12.672%   $216.6908   $216.69   $216.70   $216.70  
  Purchase #3 $50.31   11.145%   $55.917   $55.92   $55.90   $55.90  
  Purchase #4 $229.40   4.625%   $240.0098   $240.01   $240.00   $240.00  
  Purchase #5 $10.78   12.535%   $12.1313   $12.13   $12.15   $12.10  
  Purchase #6 $246.88   10.154%   $271.9482   $271.95   $271.95   $271.90  
  Purchase #7 $241.86   12.797%   $272.8108   $272.81   $272.80   $272.80  
  7 purchase totals = $1,178.41       $1,303.4893   $1,303.49   $1,303.50   $1,303.40