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 $114.78   3.363%   $118.6401   $118.64   $118.65   $118.60  
  Purchase #2 $42.69   8.525%   $46.3293   $46.33   $46.35   $46.30  
  Purchase #3 $52.85   8.147%   $57.1557   $57.16   $57.15   $57.20  
  Purchase #4 $40.43   7.819%   $43.5912   $43.59   $43.60   $43.60  
  Purchase #5 $16.42   5.807%   $17.3735   $17.37   $17.35   $17.40  
  Purchase #6 $8.69   9.362%   $9.5036   $9.50   $9.50   $9.50  
  Purchase #7 $248.62   7.623%   $267.5723   $267.57   $267.55   $267.60  
  7 purchase totals = $524.48       $560.1657   $560.16   $560.15   $560.20