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 $62.25   8.447%   $67.5083   $67.51   $67.50   $67.50  
  Purchase #2 $186.34   7.861%   $200.9882   $200.99   $201.00   $201.00  
  Purchase #3 $32.83   8.472%   $35.6114   $35.61   $35.60   $35.60  
  Purchase #4 $226.48   7.758%   $244.0503   $244.05   $244.05   $244.10  
  Purchase #5 $49.83   7.256%   $53.4457   $53.45   $53.45   $53.40  
  Purchase #6 $72.38   10.869%   $80.247   $80.25   $80.25   $80.20  
  Purchase #7 $52.91   6.793%   $56.5042   $56.50   $56.50   $56.50  
  7 purchase totals = $683.02       $738.3551   $738.36   $738.35   $738.30