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 $43.92   8.676%   $47.7305   $47.73   $47.75   $47.70  
  Purchase #2 $247.99   4.702%   $259.6505   $259.65   $259.65   $259.70  
  Purchase #3 $217.77   12.204%   $244.3467   $244.35   $244.35   $244.30  
  Purchase #4 $25.63   12.501%   $28.834   $28.83   $28.85   $28.80  
  Purchase #5 $47.40   6.758%   $50.6033   $50.60   $50.60   $50.60  
  Purchase #6 $128.75   7.538%   $138.4552   $138.46   $138.45   $138.50  
  Purchase #7 $138.63   7.828%   $149.482   $149.48   $149.50   $149.50  
  7 purchase totals = $850.09       $919.1022   $919.10   $919.15   $919.10