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	$48.54	6.102%	$51.5019	$51.50	$51.50	$51.50
Purchase #2	$56.71	10.241%	$62.5177	$62.52	$62.50	$62.50
Purchase #3	$56.45	7.115%	$60.4664	$60.47	$60.45	$60.50
Purchase #4	$47.33	13.301%	$53.6254	$53.63	$53.65	$53.60
Purchase #5	$150.72	7.306%	$161.7316	$161.73	$161.75	$161.70
Purchase #6	$218.67	10.743%	$242.1617	$242.16	$242.15	$242.20
Purchase #7	$16.74	10.279%	$18.4607	$18.46	$18.45	$18.50
7 purchase totals =	$595.16		$650.4654	$650.47	$650.45	$650.50