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 $97.85   8.299%   $105.9706   $105.97   $105.95   $106.00  
  Purchase #2 $153.79   5.811%   $162.7267   $162.73   $162.75   $162.70  
  Purchase #3 $90.40   12.874%   $102.0381   $102.04   $102.05   $102.00  
  Purchase #4 $250.28   9.852%   $274.9376   $274.94   $274.95   $274.90  
  Purchase #5 $76.88   13.731%   $87.4364   $87.44   $87.45   $87.40  
  Purchase #6 $50.80   12.157%   $56.9758   $56.98   $57.00   $57.00  
  Purchase #7 $59.63   4.208%   $62.1392   $62.14   $62.15   $62.10  
  7 purchase totals = $779.63       $852.2244   $852.24   $852.30   $852.10