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 $176.39   11.178%   $196.1069   $196.11   $196.10   $196.10  
  Purchase #2 $206.83   10.141%   $227.8046   $227.80   $227.80   $227.80  
  Purchase #3 $75.35   13.654%   $85.6383   $85.64   $85.65   $85.60  
  Purchase #4 $244.46   6.183%   $259.575   $259.58   $259.60   $259.60  
  Purchase #5 $115.28   6.460%   $122.7271   $122.73   $122.75   $122.70  
  Purchase #6 $117.54   11.222%   $130.7303   $130.73   $130.75   $130.70  
  Purchase #7 $245.48   8.729%   $266.9079   $266.91   $266.90   $266.90  
  7 purchase totals = $1,181.33       $1,289.4901   $1,289.50   $1,289.55   $1,289.40