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	$79.91	10.174%	$88.04	$88.04	$88.05	$88.00
Purchase #2	$115.48	10.121%	$127.1677	$127.17	$127.15	$127.20
Purchase #3	$96.29	7.366%	$103.3827	$103.38	$103.40	$103.40
Purchase #4	$5.94	13.661%	$6.7515	$6.75	$6.75	$6.80
Purchase #5	$239.33	11.414%	$266.6471	$266.65	$266.65	$266.60
Purchase #6	$133.96	8.154%	$144.8831	$144.88	$144.90	$144.90
Purchase #7	$35.67	4.521%	$37.2826	$37.28	$37.30	$37.30
7 purchase totals =	$706.58		$774.1547	$774.15	$774.20	$774.20