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	$71.61	12.793%	$80.7711	$80.77	$80.75	$80.80
Purchase #2	$209.48	13.651%	$238.0761	$238.08	$238.10	$238.10
Purchase #3	$53.28	6.304%	$56.6388	$56.64	$56.65	$56.60
Purchase #4	$107.69	10.215%	$118.6905	$118.69	$118.70	$118.70
Purchase #5	$217.54	4.365%	$227.0356	$227.04	$227.05	$227.00
Purchase #6	$27.53	3.846%	$28.5888	$28.59	$28.60	$28.60
Purchase #7	$238.73	12.549%	$268.6882	$268.69	$268.70	$268.70
7 purchase totals =	$925.86		$1,018.4891	$1,018.50	$1,018.55	$1,018.50