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 $15.84   3.612%   $16.4121   $16.41   $16.40   $16.40  
  Purchase #2 $245.78   9.805%   $269.8787   $269.88   $269.90   $269.90  
  Purchase #3 $23.27   11.681%   $25.9882   $25.99   $26.00   $26.00  
  Purchase #4 $94.34   11.413%   $105.107   $105.11   $105.10   $105.10  
  Purchase #5 $248.34   4.447%   $259.3837   $259.38   $259.40   $259.40  
  Purchase #6 $241.98   5.143%   $254.425   $254.43   $254.45   $254.40  
  Purchase #7 $155.68   13.108%   $176.0865   $176.09   $176.10   $176.10  
  7 purchase totals = $1,025.23       $1,107.2812   $1,107.29   $1,107.35   $1,107.30