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 $173.71   13.175%   $196.5963   $196.60   $196.60   $196.60  
  Purchase #2 $152.86   6.617%   $162.9747   $162.97   $162.95   $163.00  
  Purchase #3 $72.25   10.286%   $79.6816   $79.68   $79.70   $79.70  
  Purchase #4 $57.51   9.860%   $63.1805   $63.18   $63.20   $63.20  
  Purchase #5 $162.46   13.398%   $184.2264   $184.23   $184.25   $184.20  
  Purchase #6 $172.57   3.422%   $178.4753   $178.48   $178.50   $178.50  
  Purchase #7 $122.55   10.325%   $135.2033   $135.20   $135.20   $135.20  
  7 purchase totals = $913.91       $1,000.3381   $1,000.34   $1,000.40   $1,000.40