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 $215.70   13.241%   $244.2608   $244.26   $244.25   $244.30  
  Purchase #2 $31.61   11.466%   $35.2344   $35.23   $35.25   $35.20  
  Purchase #3 $114.44   12.302%   $128.5184   $128.52   $128.50   $128.50  
  Purchase #4 $208.57   4.350%   $217.6428   $217.64   $217.65   $217.60  
  Purchase #5 $43.51   7.504%   $46.775   $46.78   $46.80   $46.80  
  Purchase #6 $94.48   4.783%   $98.999   $99.00   $99.00   $99.00  
  Purchase #7 $239.49   9.145%   $261.3914   $261.39   $261.40   $261.40  
  7 purchase totals = $947.80       $1,032.8218   $1,032.82   $1,032.85   $1,032.80