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 $214.98   11.274%   $239.2168   $239.22   $239.20   $239.20  
  Purchase #2 $79.41   7.852%   $85.6453   $85.65   $85.65   $85.60  
  Purchase #3 $15.35   13.356%   $17.4001   $17.40   $17.40   $17.40  
  Purchase #4 $208.79   13.729%   $237.4548   $237.45   $237.45   $237.50  
  Purchase #5 $157.36   5.168%   $165.4924   $165.49   $165.50   $165.50  
  Purchase #6 $123.54   9.430%   $135.1898   $135.19   $135.20   $135.20  
  Purchase #7 $224.68   6.194%   $238.5967   $238.60   $238.60   $238.60  
  7 purchase totals = $1,024.11       $1,118.9959   $1,119.00   $1,119.00   $1,119.00