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	$57.93	6.663%	$61.7899	$61.79	$61.80	$61.80
Purchase #2	$75.68	4.672%	$79.2158	$79.22	$79.20	$79.20
Purchase #3	$88.70	13.370%	$100.5592	$100.56	$100.55	$100.60
Purchase #4	$106.71	5.814%	$112.9141	$112.91	$112.90	$112.90
Purchase #5	$68.76	13.816%	$78.2599	$78.26	$78.25	$78.30
Purchase #6	$55.59	4.476%	$58.0782	$58.08	$58.10	$58.10
Purchase #7	$52.85	4.769%	$55.3704	$55.37	$55.35	$55.40
7 purchase totals =	$506.22		$546.1875	$546.19	$546.15	$546.30