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 $227.37   8.746%   $247.2558   $247.26   $247.25   $247.30  
  Purchase #2 $174.50   9.508%   $191.0915   $191.09   $191.10   $191.10  
  Purchase #3 $177.74   13.576%   $201.87   $201.87   $201.85   $201.90  
  Purchase #4 $24.63   10.611%   $27.2435   $27.24   $27.25   $27.20  
  Purchase #5 $183.27   12.558%   $206.285   $206.29   $206.30   $206.30  
  Purchase #6 $14.96   7.556%   $16.0904   $16.09   $16.10   $16.10  
  Purchase #7 $115.96   4.655%   $121.3579   $121.36   $121.35   $121.40  
  7 purchase totals = $918.43       $1,011.1941   $1,011.20   $1,011.20   $1,011.30