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 $86.69   11.154%   $96.3594   $96.36   $96.35   $96.40  
  Purchase #2 $62.77   6.338%   $66.7484   $66.75   $66.75   $66.70  
  Purchase #3 $101.34   10.179%   $111.6554   $111.66   $111.65   $111.70  
  Purchase #4 $219.28   12.523%   $246.7404   $246.74   $246.75   $246.70  
  Purchase #5 $39.97   8.175%   $43.2375   $43.24   $43.25   $43.20  
  Purchase #6 $104.65   9.572%   $114.6671   $114.67   $114.65   $114.70  
  Purchase #7 $121.86   8.225%   $131.883   $131.88   $131.90   $131.90  
  7 purchase totals = $736.56       $811.2912   $811.30   $811.30   $811.30