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 $227.56   11.326%   $253.3334   $253.33   $253.35   $253.30  
  Purchase #2 $183.65   4.344%   $191.6278   $191.63   $191.65   $191.60  
  Purchase #3 $60.99   4.600%   $63.7955   $63.80   $63.80   $63.80  
  Purchase #4 $61.90   8.478%   $67.1479   $67.15   $67.15   $67.10  
  Purchase #5 $175.49   8.341%   $190.1276   $190.13   $190.15   $190.10  
  Purchase #6 $220.68   12.703%   $248.713   $248.71   $248.70   $248.70  
  Purchase #7 $69.29   10.597%   $76.6327   $76.63   $76.65   $76.60  
  7 purchase totals = $999.56       $1,091.3779   $1,091.38   $1,091.45   $1,091.20