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 $95.83   13.314%   $108.5888   $108.59   $108.60   $108.60  
  Purchase #2 $169.25   13.636%   $192.3289   $192.33   $192.35   $192.30  
  Purchase #3 $116.94   6.662%   $124.7305   $124.73   $124.75   $124.70  
  Purchase #4 $52.77   5.384%   $55.6111   $55.61   $55.60   $55.60  
  Purchase #5 $46.74   5.660%   $49.3855   $49.39   $49.40   $49.40  
  Purchase #6 $237.47   11.246%   $264.1759   $264.18   $264.20   $264.20  
  Purchase #7 $6.62   12.681%   $7.4595   $7.46   $7.45   $7.50  
  7 purchase totals = $725.62       $802.2802   $802.29   $802.35   $802.30