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 $85.67   13.827%   $97.5156   $97.52   $97.50   $97.50  
  Purchase #2 $196.48   13.873%   $223.7377   $223.74   $223.75   $223.70  
  Purchase #3 $84.84   5.465%   $89.4765   $89.48   $89.50   $89.50  
  Purchase #4 $244.94   13.559%   $278.1514   $278.15   $278.15   $278.20  
  Purchase #5 $171.83   13.776%   $195.5013   $195.50   $195.50   $195.50  
  Purchase #6 $63.88   10.831%   $70.7988   $70.80   $70.80   $70.80  
  Purchase #7 $162.88   12.117%   $182.6162   $182.62   $182.60   $182.60  
  7 purchase totals = $1,010.52       $1,137.7975   $1,137.81   $1,137.80   $1,137.80