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 $55.93   12.677%   $63.0202   $63.02   $63.00   $63.00  
  Purchase #2 $163.29   13.758%   $185.7554   $185.76   $185.75   $185.80  
  Purchase #3 $189.46   4.807%   $198.5673   $198.57   $198.55   $198.60  
  Purchase #4 $219.41   3.633%   $227.3812   $227.38   $227.40   $227.40  
  Purchase #5 $175.88   8.613%   $191.0285   $191.03   $191.05   $191.00  
  Purchase #6 $215.37   12.316%   $241.895   $241.90   $241.90   $241.90  
  Purchase #7 $9.40   10.435%   $10.3809   $10.38   $10.40   $10.40  
  7 purchase totals = $1,028.74       $1,118.0285   $1,118.04   $1,118.05   $1,118.10