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	$69.73	12.797%	$78.6533	$78.65	$78.65	$78.70
Purchase #2	$106.53	7.841%	$114.883	$114.88	$114.90	$114.90
Purchase #3	$18.79	7.824%	$20.2601	$20.26	$20.25	$20.30
Purchase #4	$15.35	13.859%	$17.4774	$17.48	$17.50	$17.50
Purchase #5	$44.72	8.689%	$48.6057	$48.61	$48.60	$48.60
Purchase #6	$80.64	13.178%	$91.2667	$91.27	$91.25	$91.30
Purchase #7	$142.57	6.725%	$152.1578	$152.16	$152.15	$152.20
7 purchase totals =	$478.33		$523.3040	$523.31	$523.30	$523.50