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 $248.55   3.624%   $257.5575   $257.56   $257.55   $257.60  
  Purchase #2 $89.30   9.341%   $97.6415   $97.64   $97.65   $97.60  
  Purchase #3 $172.41   13.447%   $195.594   $195.59   $195.60   $195.60  
  Purchase #4 $159.40   9.666%   $174.8076   $174.81   $174.80   $174.80  
  Purchase #5 $239.60   3.294%   $247.4924   $247.49   $247.50   $247.50  
  Purchase #6 $205.94   10.823%   $228.2289   $228.23   $228.25   $228.20  
  Purchase #7 $47.71   7.263%   $51.1752   $51.18   $51.20   $51.20  
  7 purchase totals = $1,162.91       $1,252.4971   $1,252.50   $1,252.55   $1,252.50