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	$47.30	12.682%	$53.2986	$53.30	$53.30	$53.30
Purchase #2	$145.31	3.857%	$150.9146	$150.91	$150.90	$150.90
Purchase #3	$28.59	4.635%	$29.9151	$29.92	$29.90	$29.90
Purchase #4	$151.90	12.156%	$170.365	$170.37	$170.35	$170.40
Purchase #5	$49.45	5.816%	$52.326	$52.33	$52.35	$52.30
Purchase #6	$31.89	9.773%	$35.0066	$35.01	$35.00	$35.00
Purchase #7	$102.35	7.294%	$109.8154	$109.82	$109.80	$109.80
7 purchase totals =	$556.79		$601.6413	$601.66	$601.60	$601.60