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 $250.92   7.217%   $269.0289   $269.03   $269.05   $269.00  
  Purchase #2 $213.88   4.370%   $223.2266   $223.23   $223.25   $223.20  
  Purchase #3 $117.68   6.402%   $125.2139   $125.21   $125.20   $125.20  
  Purchase #4 $24.60   9.198%   $26.8627   $26.86   $26.85   $26.90  
  Purchase #5 $236.41   4.271%   $246.5071   $246.51   $246.50   $246.50  
  Purchase #6 $108.51   10.458%   $119.858   $119.86   $119.85   $119.90  
  Purchase #7 $73.37   11.657%   $81.9227   $81.92   $81.90   $81.90  
  7 purchase totals = $1,025.37       $1,092.6199   $1,092.62   $1,092.60   $1,092.60