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 $208.36   11.712%   $232.7631   $232.76   $232.75   $232.80  
  Purchase #2 $33.49   6.240%   $35.5798   $35.58   $35.60   $35.60  
  Purchase #3 $198.65   10.547%   $219.6016   $219.60   $219.60   $219.60  
  Purchase #4 $28.87   13.387%   $32.7348   $32.73   $32.75   $32.70  
  Purchase #5 $33.93   10.709%   $37.5636   $37.56   $37.55   $37.60  
  Purchase #6 $126.30   11.605%   $140.9571   $140.96   $140.95   $141.00  
  Purchase #7 $27.61   11.752%   $30.8547   $30.85   $30.85   $30.90  
  7 purchase totals = $657.21       $730.0547   $730.04   $730.05   $730.20