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 $191.47   13.438%   $217.1997   $217.20   $217.20   $217.20  
  Purchase #2 $185.68   8.444%   $201.3588   $201.36   $201.35   $201.40  
  Purchase #3 $154.27   8.697%   $167.6869   $167.69   $167.70   $167.70  
  Purchase #4 $250.89   7.860%   $270.61   $270.61   $270.60   $270.60  
  Purchase #5 $17.60   9.227%   $19.224   $19.22   $19.20   $19.20  
  Purchase #6 $166.46   4.780%   $174.4168   $174.42   $174.40   $174.40  
  Purchase #7 $51.30   11.339%   $57.1169   $57.12   $57.10   $57.10  
  7 purchase totals = $1,017.67       $1,107.6131   $1,107.62   $1,107.55   $1,107.60