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	$99.41	10.253%	$109.6025	$109.60	$109.60	$109.60
Purchase #2	$67.64	11.841%	$75.6493	$75.65	$75.65	$75.60
Purchase #3	$11.83	9.216%	$12.9203	$12.92	$12.90	$12.90
Purchase #4	$220.81	10.264%	$243.4739	$243.47	$243.45	$243.50
Purchase #5	$173.32	13.237%	$196.2624	$196.26	$196.25	$196.30
Purchase #6	$78.95	11.661%	$88.1564	$88.16	$88.15	$88.20
Purchase #7	$56.90	10.569%	$62.9138	$62.91	$62.90	$62.90
7 purchase totals =	$708.86		$788.9786	$788.97	$788.90	$789.00