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 $206.35   5.480%   $217.658   $217.66   $217.65   $217.70  
  Purchase #2 $231.46   12.306%   $259.9435   $259.94   $259.95   $259.90  
  Purchase #3 $101.45   6.636%   $108.1822   $108.18   $108.20   $108.20  
  Purchase #4 $177.86   12.400%   $199.9146   $199.91   $199.90   $199.90  
  Purchase #5 $174.95   11.711%   $195.4384   $195.44   $195.45   $195.40  
  Purchase #6 $15.86   5.688%   $16.7621   $16.76   $16.75   $16.80  
  Purchase #7 $59.70   12.576%   $67.2079   $67.21   $67.20   $67.20  
  7 purchase totals = $967.63       $1,065.1067   $1,065.10   $1,065.10   $1,065.10