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	$157.27	6.361%	$167.2739	$167.27	$167.25	$167.30
Purchase #2	$192.72	7.335%	$206.856	$206.86	$206.85	$206.90
Purchase #3	$205.98	13.543%	$233.8759	$233.88	$233.90	$233.90
Purchase #4	$249.82	4.399%	$260.8096	$260.81	$260.80	$260.80
Purchase #5	$156.54	7.786%	$168.7282	$168.73	$168.75	$168.70
Purchase #6	$55.30	9.789%	$60.7133	$60.71	$60.70	$60.70
Purchase #7	$209.43	6.224%	$222.4649	$222.46	$222.45	$222.50
7 purchase totals =	$1,227.06		$1,320.7218	$1,320.72	$1,320.70	$1,320.80