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 $239.44   10.853%   $265.4264   $265.43   $265.45   $265.40  
  Purchase #2 $215.82   4.409%   $225.3355   $225.34   $225.35   $225.30  
  Purchase #3 $113.27   6.412%   $120.5329   $120.53   $120.55   $120.50  
  Purchase #4 $198.93   3.647%   $206.185   $206.19   $206.20   $206.20  
  Purchase #5 $177.67   9.366%   $194.3106   $194.31   $194.30   $194.30  
  Purchase #6 $40.30   3.227%   $41.6005   $41.60   $41.60   $41.60  
  Purchase #7 $15.63   3.385%   $16.1591   $16.16   $16.15   $16.20  
  7 purchase totals = $1,001.06       $1,069.5500   $1,069.56   $1,069.60   $1,069.50