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	$142.72	7.281%	$153.1114	$153.11	$153.10	$153.10
Purchase #2	$121.67	12.304%	$136.6403	$136.64	$136.65	$136.60
Purchase #3	$88.99	11.557%	$99.2746	$99.27	$99.25	$99.30
Purchase #4	$151.61	10.742%	$167.8959	$167.90	$167.90	$167.90
Purchase #5	$96.78	13.402%	$109.7505	$109.75	$109.75	$109.80
Purchase #6	$150.33	13.173%	$170.133	$170.13	$170.15	$170.10
Purchase #7	$228.65	11.447%	$254.8236	$254.82	$254.80	$254.80
7 purchase totals =	$980.75		$1,091.6293	$1,091.62	$1,091.60	$1,091.60