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 $50.92   13.162%   $57.6221   $57.62   $57.60   $57.60  
  Purchase #2 $202.66   10.298%   $223.5299   $223.53   $223.55   $223.50  
  Purchase #3 $153.91   10.854%   $170.6154   $170.62   $170.60   $170.60  
  Purchase #4 $105.29   9.102%   $114.8735   $114.87   $114.85   $114.90  
  Purchase #5 $107.66   5.814%   $113.9194   $113.92   $113.90   $113.90  
  Purchase #6 $135.72   11.111%   $150.7998   $150.80   $150.80   $150.80  
  Purchase #7 $72.41   6.159%   $76.8697   $76.87   $76.85   $76.90  
  7 purchase totals = $828.57       $908.2298   $908.23   $908.15   $908.20