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 $218.99   10.808%   $242.6584   $242.66   $242.65   $242.70  
  Purchase #2 $69.37   9.571%   $76.0094   $76.01   $76.00   $76.00  
  Purchase #3 $116.36   11.275%   $129.4796   $129.48   $129.50   $129.50  
  Purchase #4 $201.51   9.226%   $220.1013   $220.10   $220.10   $220.10  
  Purchase #5 $142.25   8.559%   $154.4252   $154.43   $154.45   $154.40  
  Purchase #6 $179.82   10.355%   $198.4404   $198.44   $198.45   $198.40  
  Purchase #7 $112.61   12.860%   $127.0916   $127.09   $127.10   $127.10  
  7 purchase totals = $1,040.91       $1,148.2059   $1,148.21   $1,148.25   $1,148.20