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	$153.73	12.383%	$172.7664	$172.77	$172.75	$172.80
Purchase #2	$55.48	13.109%	$62.7529	$62.75	$62.75	$62.80
Purchase #3	$25.97	3.683%	$26.9265	$26.93	$26.95	$26.90
Purchase #4	$69.54	12.285%	$78.083	$78.08	$78.10	$78.10
Purchase #5	$85.72	6.342%	$91.1564	$91.16	$91.15	$91.20
Purchase #6	$157.44	6.428%	$167.5602	$167.56	$167.55	$167.60
Purchase #7	$94.29	4.594%	$98.6217	$98.62	$98.60	$98.60
7 purchase totals =	$642.17		$697.8671	$697.87	$697.85	$698.00