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 $109.44   9.601%   $119.9473   $119.95   $119.95   $119.90  
  Purchase #2 $61.64   13.412%   $69.9072   $69.91   $69.90   $69.90  
  Purchase #3 $243.73   9.187%   $266.1215   $266.12   $266.10   $266.10  
  Purchase #4 $79.76   13.205%   $90.2923   $90.29   $90.30   $90.30  
  Purchase #5 $95.97   8.260%   $103.8971   $103.90   $103.90   $103.90  
  Purchase #6 $230.31   8.732%   $250.4207   $250.42   $250.40   $250.40  
  Purchase #7 $202.43   13.678%   $230.1184   $230.12   $230.10   $230.10  
  7 purchase totals = $1,023.28       $1,130.7045   $1,130.71   $1,130.65   $1,130.60