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 $234.49   7.582%   $252.269   $252.27   $252.25   $252.30  
  Purchase #2 $135.70   3.660%   $140.6666   $140.67   $140.65   $140.70  
  Purchase #3 $83.58   7.398%   $89.7632   $89.76   $89.75   $89.80  
  Purchase #4 $224.43   8.203%   $242.84   $242.84   $242.85   $242.80  
  Purchase #5 $241.79   11.340%   $269.209   $269.21   $269.20   $269.20  
  Purchase #6 $206.90   8.236%   $223.9403   $223.94   $223.95   $223.90  
  Purchase #7 $71.42   10.227%   $78.7241   $78.72   $78.70   $78.70  
  7 purchase totals = $1,198.31       $1,297.4122   $1,297.41   $1,297.35   $1,297.40