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 $97.57   6.433%   $103.8467   $103.85   $103.85   $103.80  
  Purchase #2 $21.65   9.412%   $23.6877   $23.69   $23.70   $23.70  
  Purchase #3 $163.36   7.557%   $175.7051   $175.71   $175.70   $175.70  
  Purchase #4 $23.98   6.312%   $25.4936   $25.49   $25.50   $25.50  
  Purchase #5 $166.75   10.754%   $184.6823   $184.68   $184.70   $184.70  
  Purchase #6 $134.91   6.511%   $143.694   $143.69   $143.70   $143.70  
  Purchase #7 $230.80   3.767%   $239.4942   $239.49   $239.50   $239.50  
  7 purchase totals = $839.02       $896.6036   $896.60   $896.65   $896.60