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	$90.28	6.448%	$96.1013	$96.10	$96.10	$96.10
Purchase #2	$40.96	10.504%	$45.2624	$45.26	$45.25	$45.30
Purchase #3	$114.80	10.728%	$127.1157	$127.12	$127.10	$127.10
Purchase #4	$33.66	12.792%	$37.9658	$37.97	$37.95	$38.00
Purchase #5	$113.62	6.295%	$120.7724	$120.77	$120.75	$120.80
Purchase #6	$235.63	12.690%	$265.5314	$265.53	$265.55	$265.50
Purchase #7	$116.52	11.181%	$129.5481	$129.55	$129.55	$129.50
7 purchase totals =	$745.47		$822.2971	$822.30	$822.25	$822.30