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 $53.26   12.329%   $59.8264   $59.83   $59.85   $59.80  
  Purchase #2 $30.34   12.245%   $34.0551   $34.06   $34.05   $34.10  
  Purchase #3 $162.96   12.105%   $182.6863   $182.69   $182.70   $182.70  
  Purchase #4 $67.83   8.400%   $73.5277   $73.53   $73.55   $73.50  
  Purchase #5 $249.68   6.285%   $265.3724   $265.37   $265.35   $265.40  
  Purchase #6 $193.44   9.487%   $211.7917   $211.79   $211.80   $211.80  
  Purchase #7 $184.61   10.353%   $203.7227   $203.72   $203.70   $203.70  
  7 purchase totals = $942.12       $1,030.9823   $1,030.99   $1,031.00   $1,031.00