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	$36.56	9.691%	$40.103	$40.10	$40.10	$40.10
Purchase #2	$108.53	11.454%	$120.961	$120.96	$120.95	$121.00
Purchase #3	$118.90	7.117%	$127.3621	$127.36	$127.35	$127.40
Purchase #4	$34.43	13.693%	$39.1445	$39.14	$39.15	$39.10
Purchase #5	$187.95	13.565%	$213.4454	$213.45	$213.45	$213.40
Purchase #6	$83.48	10.402%	$92.1636	$92.16	$92.15	$92.20
Purchase #7	$90.53	6.861%	$96.7413	$96.74	$96.75	$96.70
7 purchase totals =	$660.38		$729.9209	$729.91	$729.90	$729.90