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 $224.25   6.708%   $239.2927   $239.29   $239.30   $239.30  
  Purchase #2 $208.29   13.147%   $235.6739   $235.67   $235.65   $235.70  
  Purchase #3 $220.26   8.227%   $238.3808   $238.38   $238.40   $238.40  
  Purchase #4 $215.47   5.619%   $227.5773   $227.58   $227.60   $227.60  
  Purchase #5 $211.93   13.679%   $240.9199   $240.92   $240.90   $240.90  
  Purchase #6 $11.91   11.846%   $13.3209   $13.32   $13.30   $13.30  
  Purchase #7 $222.56   8.196%   $240.801   $240.80   $240.80   $240.80  
  7 purchase totals = $1,314.67       $1,435.9665   $1,435.96   $1,435.95   $1,436.00