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 $200.44   3.411%   $207.277   $207.28   $207.30   $207.30  
  Purchase #2 $165.96   11.839%   $185.608   $185.61   $185.60   $185.60  
  Purchase #3 $189.97   7.788%   $204.7649   $204.76   $204.75   $204.80  
  Purchase #4 $50.77   5.178%   $53.3989   $53.40   $53.40   $53.40  
  Purchase #5 $192.55   11.693%   $215.0649   $215.06   $215.05   $215.10  
  Purchase #6 $110.49   10.798%   $122.4207   $122.42   $122.40   $122.40  
  Purchase #7 $56.75   9.329%   $62.0442   $62.04   $62.05   $62.00  
  7 purchase totals = $966.93       $1,050.5786   $1,050.57   $1,050.55   $1,050.60