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 $207.90   13.798%   $236.586   $236.59   $236.60   $236.60  
  Purchase #2 $38.34   12.248%   $43.0359   $43.04   $43.05   $43.00  
  Purchase #3 $168.37   6.196%   $178.8022   $178.80   $178.80   $178.80  
  Purchase #4 $91.99   3.276%   $95.0036   $95.00   $95.00   $95.00  
  Purchase #5 $23.29   11.627%   $25.9979   $26.00   $26.00   $26.00  
  Purchase #6 $230.79   10.233%   $254.4067   $254.41   $254.40   $254.40  
  Purchase #7 $185.69   11.553%   $207.1428   $207.14   $207.15   $207.10  
  7 purchase totals = $946.37       $1,040.9751   $1,040.98   $1,041.00   $1,040.90