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	$72.62	9.258%	$79.3432	$79.34	$79.35	$79.30
Purchase #2	$106.45	7.138%	$114.0484	$114.05	$114.05	$114.00
Purchase #3	$61.49	12.651%	$69.2691	$69.27	$69.25	$69.30
Purchase #4	$99.53	11.472%	$110.9481	$110.95	$110.95	$110.90
Purchase #5	$127.70	10.658%	$141.3103	$141.31	$141.30	$141.30
Purchase #6	$101.63	9.726%	$111.5145	$111.51	$111.50	$111.50
Purchase #7	$54.31	5.861%	$57.4931	$57.49	$57.50	$57.50
7 purchase totals =	$623.73		$683.9267	$683.92	$683.90	$683.80