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 $225.69   5.151%   $237.3153   $237.32   $237.30   $237.30  
  Purchase #2 $124.46   9.613%   $136.4243   $136.42   $136.40   $136.40  
  Purchase #3 $186.84   4.394%   $195.0497   $195.05   $195.05   $195.00  
  Purchase #4 $77.73   4.661%   $81.353   $81.35   $81.35   $81.40  
  Purchase #5 $173.39   5.535%   $182.9871   $182.99   $183.00   $183.00  
  Purchase #6 $247.73   9.811%   $272.0348   $272.03   $272.05   $272.00  
  Purchase #7 $130.55   4.620%   $136.5814   $136.58   $136.60   $136.60  
  7 purchase totals = $1,166.39       $1,241.7456   $1,241.74   $1,241.75   $1,241.70