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 $215.39   9.627%   $236.1256   $236.13   $236.15   $236.10  
  Purchase #2 $67.33   9.279%   $73.5776   $73.58   $73.60   $73.60  
  Purchase #3 $172.53   5.473%   $181.9726   $181.97   $181.95   $182.00  
  Purchase #4 $221.59   10.295%   $244.4027   $244.40   $244.40   $244.40  
  Purchase #5 $203.51   11.789%   $227.5018   $227.50   $227.50   $227.50  
  Purchase #6 $242.32   5.113%   $254.7098   $254.71   $254.70   $254.70  
  Purchase #7 $17.47   6.495%   $18.6047   $18.60   $18.60   $18.60  
  7 purchase totals = $1,140.14       $1,236.8948   $1,236.89   $1,236.90   $1,236.90