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 $185.53   11.725%   $207.2834   $207.28   $207.30   $207.30  
  Purchase #2 $220.73   13.365%   $250.2306   $250.23   $250.25   $250.20  
  Purchase #3 $93.86   6.145%   $99.6277   $99.63   $99.65   $99.60  
  Purchase #4 $216.34   12.309%   $242.9693   $242.97   $242.95   $243.00  
  Purchase #5 $246.76   5.264%   $259.7494   $259.75   $259.75   $259.70  
  Purchase #6 $147.67   12.303%   $165.8378   $165.84   $165.85   $165.80  
  Purchase #7 $124.57   6.736%   $132.961   $132.96   $132.95   $133.00  
  7 purchase totals = $1,235.46       $1,358.6592   $1,358.66   $1,358.70   $1,358.60