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 $86.41   8.295%   $93.5777   $93.58   $93.60   $93.60  
  Purchase #2 $166.62   12.725%   $187.8224   $187.82   $187.80   $187.80  
  Purchase #3 $219.85   13.136%   $248.7295   $248.73   $248.75   $248.70  
  Purchase #4 $86.39   5.474%   $91.119   $91.12   $91.10   $91.10  
  Purchase #5 $118.32   8.578%   $128.4695   $128.47   $128.45   $128.50  
  Purchase #6 $63.39   9.623%   $69.49   $69.49   $69.50   $69.50  
  Purchase #7 $150.75   7.679%   $162.3261   $162.33   $162.35   $162.30  
  7 purchase totals = $891.73       $981.5342   $981.54   $981.55   $981.50