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	$40.27	12.488%	$45.2989	$45.30	$45.30	$45.30
Purchase #2	$80.98	10.447%	$89.44	$89.44	$89.45	$89.40
Purchase #3	$233.35	12.465%	$262.4371	$262.44	$262.45	$262.40
Purchase #4	$23.40	13.612%	$26.5852	$26.59	$26.60	$26.60
Purchase #5	$207.77	7.208%	$222.7461	$222.75	$222.75	$222.70
Purchase #6	$98.54	13.597%	$111.9385	$111.94	$111.95	$111.90
Purchase #7	$112.41	8.417%	$121.8715	$121.87	$121.85	$121.90
7 purchase totals =	$796.72		$880.3173	$880.33	$880.35	$880.20