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	$238.77	12.243%	$268.0026	$268.00	$268.00	$268.00
Purchase #2	$105.60	11.259%	$117.4895	$117.49	$117.50	$117.50
Purchase #3	$82.81	8.116%	$89.5309	$89.53	$89.55	$89.50
Purchase #4	$114.48	11.667%	$127.8364	$127.84	$127.85	$127.80
Purchase #5	$225.76	12.465%	$253.901	$253.90	$253.90	$253.90
Purchase #6	$118.78	12.222%	$133.2973	$133.30	$133.30	$133.30
Purchase #7	$82.33	13.350%	$93.3211	$93.32	$93.30	$93.30
7 purchase totals =	$968.53		$1,083.3788	$1,083.38	$1,083.40	$1,083.30