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 $161.49   6.197%   $171.4975   $171.50   $171.50   $171.50  
  Purchase #2 $125.26   7.863%   $135.1092   $135.11   $135.10   $135.10  
  Purchase #3 $21.32   7.491%   $22.9171   $22.92   $22.90   $22.90  
  Purchase #4 $177.48   3.551%   $183.7823   $183.78   $183.80   $183.80  
  Purchase #5 $38.83   6.408%   $41.3182   $41.32   $41.30   $41.30  
  Purchase #6 $243.36   13.361%   $275.8753   $275.88   $275.90   $275.90  
  Purchase #7 $214.70   10.398%   $237.0245   $237.02   $237.00   $237.00  
  7 purchase totals = $982.44       $1,067.5241   $1,067.53   $1,067.50   $1,067.50