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	$83.78	5.137%	$88.0838	$88.08	$88.10	$88.10
Purchase #2	$38.53	7.495%	$41.4178	$41.42	$41.40	$41.40
Purchase #3	$9.54	5.114%	$10.0279	$10.03	$10.05	$10.00
Purchase #4	$246.82	9.781%	$270.9615	$270.96	$270.95	$271.00
Purchase #5	$57.41	5.170%	$60.3781	$60.38	$60.40	$60.40
Purchase #6	$99.27	10.623%	$109.8155	$109.82	$109.80	$109.80
Purchase #7	$176.43	11.608%	$196.91	$196.91	$196.90	$196.90
7 purchase totals =	$711.78		$777.5946	$777.60	$777.60	$777.60