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	$67.92	5.209%	$71.458	$71.46	$71.45	$71.50
Purchase #2	$133.79	8.223%	$144.7916	$144.79	$144.80	$144.80
Purchase #3	$41.29	9.556%	$45.2357	$45.24	$45.25	$45.20
Purchase #4	$57.62	3.269%	$59.5036	$59.50	$59.50	$59.50
Purchase #5	$193.48	5.583%	$204.282	$204.28	$204.30	$204.30
Purchase #6	$99.64	6.641%	$106.2571	$106.26	$106.25	$106.30
Purchase #7	$54.76	3.675%	$56.7724	$56.77	$56.75	$56.80
7 purchase totals =	$648.50		$688.3004	$688.30	$688.30	$688.40