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 $247.51   11.505%   $275.986   $275.99   $276.00   $276.00  
  Purchase #2 $236.77   10.555%   $261.7611   $261.76   $261.75   $261.80  
  Purchase #3 $241.57   9.780%   $265.1955   $265.20   $265.20   $265.20  
  Purchase #4 $248.52   6.554%   $264.808   $264.81   $264.80   $264.80  
  Purchase #5 $203.42   12.588%   $229.0265   $229.03   $229.05   $229.00  
  Purchase #6 $161.54   13.262%   $182.9634   $182.96   $182.95   $183.00  
  Purchase #7 $116.62   8.779%   $126.8581   $126.86   $126.85   $126.90  
  7 purchase totals = $1,455.95       $1,606.5986   $1,606.61   $1,606.60   $1,606.70