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 $133.62   10.806%   $148.059   $148.06   $148.05   $148.10  
  Purchase #2 $206.67   12.571%   $232.6505   $232.65   $232.65   $232.70  
  Purchase #3 $72.84   8.713%   $79.1865   $79.19   $79.20   $79.20  
  Purchase #4 $173.51   7.112%   $185.85   $185.85   $185.85   $185.90  
  Purchase #5 $161.25   10.229%   $177.7443   $177.74   $177.75   $177.70  
  Purchase #6 $116.65   8.468%   $126.5279   $126.53   $126.55   $126.50  
  Purchase #7 $5.37   5.380%   $5.6589   $5.66   $5.65   $5.70  
  7 purchase totals = $869.91       $955.6771   $955.68   $955.70   $955.80