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 $215.68   11.752%   $241.0267   $241.03   $241.05   $241.00  
  Purchase #2 $133.62   9.683%   $146.5584   $146.56   $146.55   $146.60  
  Purchase #3 $146.63   3.705%   $152.0626   $152.06   $152.05   $152.10  
  Purchase #4 $199.40   11.126%   $221.5852   $221.59   $221.60   $221.60  
  Purchase #5 $61.65   3.279%   $63.6715   $63.67   $63.65   $63.70  
  Purchase #6 $199.34   8.158%   $215.6022   $215.60   $215.60   $215.60  
  Purchase #7 $108.90   13.140%   $123.2095   $123.21   $123.20   $123.20  
  7 purchase totals = $1,065.22       $1,163.7161   $1,163.72   $1,163.70   $1,163.80