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	$248.73	13.389%	$282.0325	$282.03	$282.05	$282.00
Purchase #2	$72.32	12.274%	$81.1966	$81.20	$81.20	$81.20
Purchase #3	$79.28	8.664%	$86.1488	$86.15	$86.15	$86.10
Purchase #4	$81.57	13.351%	$92.4604	$92.46	$92.45	$92.50
Purchase #5	$33.90	6.373%	$36.0604	$36.06	$36.05	$36.10
Purchase #6	$120.76	5.751%	$127.7049	$127.70	$127.70	$127.70
Purchase #7	$96.91	8.668%	$105.3102	$105.31	$105.30	$105.30
7 purchase totals =	$733.47		$810.9138	$810.91	$810.90	$810.90