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 $217.89   12.254%   $244.5902   $244.59   $244.60   $244.60  
  Purchase #2 $193.98   11.540%   $216.3653   $216.37   $216.35   $216.40  
  Purchase #3 $206.93   10.469%   $228.5935   $228.59   $228.60   $228.60  
  Purchase #4 $79.55   11.504%   $88.7014   $88.70   $88.70   $88.70  
  Purchase #5 $120.62   3.311%   $124.6137   $124.61   $124.60   $124.60  
  Purchase #6 $240.41   7.771%   $259.0923   $259.09   $259.10   $259.10  
  Purchase #7 $39.69   4.530%   $41.488   $41.49   $41.50   $41.50  
  7 purchase totals = $1,099.07       $1,203.4444   $1,203.44   $1,203.45   $1,203.50