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 $152.58   13.850%   $173.7123   $173.71   $173.70   $173.70  
  Purchase #2 $223.76   4.423%   $233.6569   $233.66   $233.65   $233.70  
  Purchase #3 $71.49   13.125%   $80.8731   $80.87   $80.85   $80.90  
  Purchase #4 $153.47   4.633%   $160.5803   $160.58   $160.60   $160.60  
  Purchase #5 $34.37   5.858%   $36.3834   $36.38   $36.40   $36.40  
  Purchase #6 $189.42   12.733%   $213.5388   $213.54   $213.55   $213.50  
  Purchase #7 $134.95   5.693%   $142.6327   $142.63   $142.65   $142.60  
  7 purchase totals = $960.04       $1,041.3775   $1,041.37   $1,041.40   $1,041.40