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 $217.59   7.473%   $233.8505   $233.85   $233.85   $233.90  
  Purchase #2 $226.42   12.857%   $255.5308   $255.53   $255.55   $255.50  
  Purchase #3 $116.63   11.102%   $129.5783   $129.58   $129.60   $129.60  
  Purchase #4 $42.39   3.817%   $44.008   $44.01   $44.00   $44.00  
  Purchase #5 $231.25   11.200%   $257.15   $257.15   $257.15   $257.20  
  Purchase #6 $93.85   9.818%   $103.0642   $103.06   $103.05   $103.10  
  Purchase #7 $24.49   7.307%   $26.2795   $26.28   $26.30   $26.30  
  7 purchase totals = $952.62       $1,049.4613   $1,049.46   $1,049.50   $1,049.60