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 $202.40   11.688%   $226.0565   $226.06   $226.05   $226.10  
  Purchase #2 $12.69   7.335%   $13.6208   $13.62   $13.60   $13.60  
  Purchase #3 $174.30   13.304%   $197.4889   $197.49   $197.50   $197.50  
  Purchase #4 $128.51   4.181%   $133.883   $133.88   $133.90   $133.90  
  Purchase #5 $50.57   11.825%   $56.5499   $56.55   $56.55   $56.50  
  Purchase #6 $68.54   13.194%   $77.5832   $77.58   $77.60   $77.60  
  Purchase #7 $197.31   10.669%   $218.361   $218.36   $218.35   $218.40  
  7 purchase totals = $834.32       $923.5433   $923.54   $923.55   $923.60