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 $241.53   12.824%   $272.5038   $272.50   $272.50   $272.50  
  Purchase #2 $182.81   11.646%   $204.1001   $204.10   $204.10   $204.10  
  Purchase #3 $56.39   5.473%   $59.4762   $59.48   $59.50   $59.50  
  Purchase #4 $119.46   13.570%   $135.6707   $135.67   $135.65   $135.70  
  Purchase #5 $234.50   3.141%   $241.8656   $241.87   $241.85   $241.90  
  Purchase #6 $150.34   11.371%   $167.4352   $167.44   $167.45   $167.40  
  Purchase #7 $151.36   6.126%   $160.6323   $160.63   $160.65   $160.60  
  7 purchase totals = $1,136.39       $1,241.6839   $1,241.69   $1,241.70   $1,241.70