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 $98.38   8.193%   $106.4403   $106.44   $106.45   $106.40  
  Purchase #2 $23.74   4.752%   $24.8681   $24.87   $24.85   $24.90  
  Purchase #3 $236.63   12.525%   $266.2679   $266.27   $266.25   $266.30  
  Purchase #4 $128.39   4.279%   $133.8838   $133.88   $133.90   $133.90  
  Purchase #5 $233.95   5.467%   $246.74   $246.74   $246.75   $246.70  
  Purchase #6 $24.68   12.111%   $27.669   $27.67   $27.65   $27.70  
  Purchase #7 $214.51   5.647%   $226.6234   $226.62   $226.60   $226.60  
  7 purchase totals = $960.28       $1,032.4925   $1,032.49   $1,032.45   $1,032.50