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 $228.58   13.716%   $259.932   $259.93   $259.95   $259.90  
  Purchase #2 $86.50   8.395%   $93.7617   $93.76   $93.75   $93.80  
  Purchase #3 $82.40   4.727%   $86.295   $86.30   $86.30   $86.30  
  Purchase #4 $184.75   4.632%   $193.3076   $193.31   $193.30   $193.30  
  Purchase #5 $245.48   12.843%   $277.007   $277.01   $277.00   $277.00  
  Purchase #6 $53.70   10.795%   $59.4969   $59.50   $59.50   $59.50  
  Purchase #7 $217.40   5.244%   $228.8005   $228.80   $228.80   $228.80  
  7 purchase totals = $1,098.81       $1,198.6007   $1,198.61   $1,198.60   $1,198.60