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 $209.92   6.694%   $223.972   $223.97   $223.95   $224.00  
  Purchase #2 $105.95   13.835%   $120.6082   $120.61   $120.60   $120.60  
  Purchase #3 $15.34   9.705%   $16.8287   $16.83   $16.85   $16.80  
  Purchase #4 $138.40   13.379%   $156.9165   $156.92   $156.90   $156.90  
  Purchase #5 $199.76   9.574%   $218.885   $218.89   $218.90   $218.90  
  Purchase #6 $232.90   6.544%   $248.141   $248.14   $248.15   $248.10  
  Purchase #7 $53.49   12.260%   $60.0479   $60.05   $60.05   $60.00  
  7 purchase totals = $955.76       $1,045.3993   $1,045.41   $1,045.40   $1,045.30