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 $109.53   13.295%   $124.092   $124.09   $124.10   $124.10  
  Purchase #2 $163.46   8.130%   $176.7493   $176.75   $176.75   $176.70  
  Purchase #3 $167.84   5.674%   $177.3632   $177.36   $177.35   $177.40  
  Purchase #4 $176.79   11.198%   $196.5869   $196.59   $196.60   $196.60  
  Purchase #5 $33.49   9.770%   $36.762   $36.76   $36.75   $36.80  
  Purchase #6 $249.98   7.158%   $267.8736   $267.87   $267.85   $267.90  
  Purchase #7 $214.90   10.274%   $236.9788   $236.98   $237.00   $237.00  
  7 purchase totals = $1,115.99       $1,216.4058   $1,216.40   $1,216.40   $1,216.50