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 $196.38   6.772%   $209.6789   $209.68   $209.70   $209.70  
  Purchase #2 $73.68   6.793%   $78.6851   $78.69   $78.70   $78.70  
  Purchase #3 $215.93   11.243%   $240.207   $240.21   $240.20   $240.20  
  Purchase #4 $181.94   7.453%   $195.5   $195.50   $195.50   $195.50  
  Purchase #5 $225.93   7.451%   $242.764   $242.76   $242.75   $242.80  
  Purchase #6 $192.28   6.260%   $204.3167   $204.32   $204.30   $204.30  
  Purchase #7 $44.31   11.405%   $49.3636   $49.36   $49.35   $49.40  
  7 purchase totals = $1,130.45       $1,220.5153   $1,220.52   $1,220.50   $1,220.60