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 $242.57   6.792%   $259.0454   $259.05   $259.05   $259.00  
  Purchase #2 $235.77   3.149%   $243.1944   $243.19   $243.20   $243.20  
  Purchase #3 $14.96   6.848%   $15.9845   $15.98   $16.00   $16.00  
  Purchase #4 $189.65   13.656%   $215.5486   $215.55   $215.55   $215.50  
  Purchase #5 $210.70   5.551%   $222.396   $222.40   $222.40   $222.40  
  Purchase #6 $226.89   6.542%   $241.7331   $241.73   $241.75   $241.70  
  Purchase #7 $137.73   8.582%   $149.55   $149.55   $149.55   $149.60  
  7 purchase totals = $1,258.27       $1,347.4520   $1,347.45   $1,347.50   $1,347.40