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 $234.46   12.106%   $262.8437   $262.84   $262.85   $262.80  
  Purchase #2 $47.57   4.848%   $49.8762   $49.88   $49.90   $49.90  
  Purchase #3 $122.52   5.305%   $129.0197   $129.02   $129.00   $129.00  
  Purchase #4 $231.72   7.188%   $248.376   $248.38   $248.40   $248.40  
  Purchase #5 $78.98   7.467%   $84.8774   $84.88   $84.90   $84.90  
  Purchase #6 $191.88   5.594%   $202.6138   $202.61   $202.60   $202.60  
  Purchase #7 $8.69   3.782%   $9.0187   $9.02   $9.00   $9.00  
  7 purchase totals = $915.82       $986.6255   $986.63   $986.65   $986.60