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	$238.89	10.152%	$263.1421	$263.14	$263.15	$263.10
Purchase #2	$63.86	9.741%	$70.0806	$70.08	$70.10	$70.10
Purchase #3	$153.30	11.787%	$171.3695	$171.37	$171.35	$171.40
Purchase #4	$76.69	13.278%	$86.8729	$86.87	$86.85	$86.90
Purchase #5	$202.53	13.352%	$229.5718	$229.57	$229.55	$229.60
Purchase #6	$250.51	5.379%	$263.9849	$263.98	$264.00	$264.00
Purchase #7	$107.38	4.179%	$111.8674	$111.87	$111.85	$111.90
7 purchase totals =	$1,093.16		$1,196.8892	$1,196.88	$1,196.85	$1,197.00