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 $62.41   12.527%   $70.2281   $70.23   $70.25   $70.20  
  Purchase #2 $139.42   6.313%   $148.2216   $148.22   $148.20   $148.20  
  Purchase #3 $173.92   5.293%   $183.1256   $183.13   $183.15   $183.10  
  Purchase #4 $241.80   11.285%   $269.0871   $269.09   $269.10   $269.10  
  Purchase #5 $48.93   4.535%   $51.149   $51.15   $51.15   $51.10  
  Purchase #6 $143.44   13.277%   $162.4845   $162.48   $162.50   $162.50  
  Purchase #7 $229.61   12.351%   $257.9691   $257.97   $257.95   $258.00  
  7 purchase totals = $1,039.53       $1,142.2650   $1,142.27   $1,142.30   $1,142.20