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 $67.85   11.134%   $75.4044   $75.40   $75.40   $75.40  
  Purchase #2 $154.74   4.688%   $161.9942   $161.99   $162.00   $162.00  
  Purchase #3 $106.85   6.776%   $114.0902   $114.09   $114.10   $114.10  
  Purchase #4 $168.61   11.124%   $187.3662   $187.37   $187.35   $187.40  
  Purchase #5 $180.31   10.102%   $198.5249   $198.52   $198.50   $198.50  
  Purchase #6 $166.42   9.643%   $182.4679   $182.47   $182.45   $182.50  
  Purchase #7 $28.86   4.869%   $30.2652   $30.27   $30.25   $30.30  
  7 purchase totals = $873.64       $950.1130   $950.11   $950.05   $950.20