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 $206.74   13.645%   $234.9497   $234.95   $234.95   $234.90  
  Purchase #2 $136.99   5.493%   $144.5149   $144.51   $144.50   $144.50  
  Purchase #3 $58.88   4.220%   $61.3647   $61.36   $61.35   $61.40  
  Purchase #4 $191.61   8.567%   $208.0252   $208.03   $208.05   $208.00  
  Purchase #5 $230.98   10.235%   $254.6208   $254.62   $254.60   $254.60  
  Purchase #6 $249.40   11.424%   $277.8915   $277.89   $277.90   $277.90  
  Purchase #7 $134.35   11.700%   $150.069   $150.07   $150.05   $150.10  
  7 purchase totals = $1,208.95       $1,331.4358   $1,331.43   $1,331.40   $1,331.40