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 $88.73   13.404%   $100.6234   $100.62   $100.60   $100.60  
  Purchase #2 $89.80   4.293%   $93.6551   $93.66   $93.65   $93.70  
  Purchase #3 $247.36   10.284%   $272.7985   $272.80   $272.80   $272.80  
  Purchase #4 $236.58   5.307%   $249.1353   $249.14   $249.15   $249.10  
  Purchase #5 $43.30   8.339%   $46.9108   $46.91   $46.90   $46.90  
  Purchase #6 $180.32   7.750%   $194.2948   $194.29   $194.30   $194.30  
  Purchase #7 $175.89   5.636%   $185.8032   $185.80   $185.80   $185.80  
  7 purchase totals = $1,061.98       $1,143.2211   $1,143.22   $1,143.20   $1,143.20