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 $96.62   8.818%   $105.14   $105.14   $105.15   $105.10  
  Purchase #2 $113.64   10.697%   $125.7961   $125.80   $125.80   $125.80  
  Purchase #3 $147.25   6.845%   $157.3293   $157.33   $157.35   $157.30  
  Purchase #4 $6.93   8.159%   $7.4954   $7.50   $7.50   $7.50  
  Purchase #5 $230.59   12.711%   $259.9003   $259.90   $259.90   $259.90  
  Purchase #6 $19.45   6.391%   $20.693   $20.69   $20.70   $20.70  
  Purchase #7 $223.42   11.147%   $248.3246   $248.32   $248.30   $248.30  
  7 purchase totals = $837.90       $924.6787   $924.68   $924.70   $924.60