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 $204.97   8.293%   $221.9682   $221.97   $221.95   $222.00  
  Purchase #2 $154.39   4.104%   $160.7262   $160.73   $160.75   $160.70  
  Purchase #3 $207.92   10.408%   $229.5603   $229.56   $229.55   $229.60  
  Purchase #4 $184.91   6.766%   $197.421   $197.42   $197.40   $197.40  
  Purchase #5 $60.51   11.870%   $67.6925   $67.69   $67.70   $67.70  
  Purchase #6 $71.40   8.863%   $77.7282   $77.73   $77.75   $77.70  
  Purchase #7 $223.58   10.211%   $246.4098   $246.41   $246.40   $246.40  
  7 purchase totals = $1,107.68       $1,201.5062   $1,201.51   $1,201.50   $1,201.50