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	$161.33	7.118%	$172.8135	$172.81	$172.80	$172.80
Purchase #2	$157.36	9.132%	$171.7301	$171.73	$171.75	$171.70
Purchase #3	$204.97	10.185%	$225.8462	$225.85	$225.85	$225.80
Purchase #4	$39.49	6.755%	$42.1575	$42.16	$42.15	$42.20
Purchase #5	$64.89	3.587%	$67.2176	$67.22	$67.20	$67.20
Purchase #6	$173.68	7.310%	$186.376	$186.38	$186.40	$186.40
Purchase #7	$60.45	3.858%	$62.7822	$62.78	$62.80	$62.80
7 purchase totals =	$862.17		$928.9231	$928.93	$928.95	$928.90