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 $31.26   11.327%   $34.8008   $34.80   $34.80   $34.80  
  Purchase #2 $74.63   11.435%   $83.1639   $83.16   $83.15   $83.20  
  Purchase #3 $168.67   8.587%   $183.1537   $183.15   $183.15   $183.20  
  Purchase #4 $91.57   5.867%   $96.9424   $96.94   $96.95   $96.90  
  Purchase #5 $118.46   11.376%   $131.936   $131.94   $131.95   $131.90  
  Purchase #6 $240.46   5.425%   $253.505   $253.51   $253.50   $253.50  
  Purchase #7 $208.97   13.767%   $237.7389   $237.74   $237.75   $237.70  
  7 purchase totals = $934.02       $1,021.2407   $1,021.24   $1,021.25   $1,021.20