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 $89.48   9.525%   $98.003   $98.00   $98.00   $98.00  
  Purchase #2 $60.40   3.803%   $62.697   $62.70   $62.70   $62.70  
  Purchase #3 $25.53   11.133%   $28.3723   $28.37   $28.35   $28.40  
  Purchase #4 $135.66   13.615%   $154.1301   $154.13   $154.15   $154.10  
  Purchase #5 $181.95   6.517%   $193.8077   $193.81   $193.80   $193.80  
  Purchase #6 $150.75   3.187%   $155.5544   $155.55   $155.55   $155.60  
  Purchase #7 $200.63   9.399%   $219.4872   $219.49   $219.50   $219.50  
  7 purchase totals = $844.40       $912.0517   $912.05   $912.05   $912.10