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 $41.92   7.271%   $44.968   $44.97   $44.95   $45.00  
  Purchase #2 $162.69   8.569%   $176.6309   $176.63   $176.65   $176.60  
  Purchase #3 $25.62   12.665%   $28.8648   $28.86   $28.85   $28.90  
  Purchase #4 $190.59   7.842%   $205.5361   $205.54   $205.55   $205.50  
  Purchase #5 $70.54   5.192%   $74.2024   $74.20   $74.20   $74.20  
  Purchase #6 $174.70   5.511%   $184.3277   $184.33   $184.35   $184.30  
  Purchase #7 $27.63   7.671%   $29.7495   $29.75   $29.75   $29.70  
  7 purchase totals = $693.69       $744.2794   $744.28   $744.30   $744.20