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 $86.47   7.460%   $92.9207   $92.92   $92.90   $92.90  
  Purchase #2 $134.34   13.768%   $152.8359   $152.84   $152.85   $152.80  
  Purchase #3 $185.54   7.541%   $199.5316   $199.53   $199.55   $199.50  
  Purchase #4 $236.63   12.730%   $266.753   $266.75   $266.75   $266.80  
  Purchase #5 $124.26   8.264%   $134.5288   $134.53   $134.55   $134.50  
  Purchase #6 $83.79   6.595%   $89.316   $89.32   $89.30   $89.30  
  Purchase #7 $67.93   4.432%   $70.9407   $70.94   $70.95   $70.90  
  7 purchase totals = $918.96       $1,006.8267   $1,006.83   $1,006.85   $1,006.70