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 $88.73   11.203%   $98.6704   $98.67   $98.65   $98.70  
  Purchase #2 $181.83   8.174%   $196.6928   $196.69   $196.70   $196.70  
  Purchase #3 $181.29   6.366%   $192.8309   $192.83   $192.85   $192.80  
  Purchase #4 $185.58   8.462%   $201.2838   $201.28   $201.30   $201.30  
  Purchase #5 $113.47   8.183%   $122.7553   $122.76   $122.75   $122.80  
  Purchase #6 $221.78   12.462%   $249.4182   $249.42   $249.40   $249.40  
  Purchase #7 $10.97   8.545%   $11.9074   $11.91   $11.90   $11.90  
  7 purchase totals = $983.65       $1,073.5588   $1,073.56   $1,073.55   $1,073.60