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 $248.76   9.863%   $273.2952   $273.30   $273.30   $273.30  
  Purchase #2 $133.60   8.385%   $144.8024   $144.80   $144.80   $144.80  
  Purchase #3 $63.73   3.301%   $65.8337   $65.83   $65.85   $65.80  
  Purchase #4 $12.97   11.403%   $14.449   $14.45   $14.45   $14.40  
  Purchase #5 $201.96   3.176%   $208.3742   $208.37   $208.35   $208.40  
  Purchase #6 $232.49   6.102%   $246.6765   $246.68   $246.70   $246.70  
  Purchase #7 $228.69   9.686%   $250.8409   $250.84   $250.85   $250.80  
  7 purchase totals = $1,122.20       $1,204.2719   $1,204.27   $1,204.30   $1,204.20