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 $113.79   10.217%   $125.4159   $125.42   $125.40   $125.40  
  Purchase #2 $124.65   13.663%   $141.6809   $141.68   $141.70   $141.70  
  Purchase #3 $167.42   3.863%   $173.8874   $173.89   $173.90   $173.90  
  Purchase #4 $153.25   7.315%   $164.4602   $164.46   $164.45   $164.50  
  Purchase #5 $199.57   8.749%   $217.0304   $217.03   $217.05   $217.00  
  Purchase #6 $130.51   8.394%   $141.465   $141.47   $141.45   $141.50  
  Purchase #7 $186.67   7.836%   $201.2975   $201.30   $201.30   $201.30  
  7 purchase totals = $1,075.86       $1,165.2373   $1,165.25   $1,165.25   $1,165.30