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	$28.45	9.759%	$31.2264	$31.23	$31.25	$31.20
Purchase #2	$144.34	11.510%	$160.9535	$160.95	$160.95	$161.00
Purchase #3	$101.38	10.178%	$111.6985	$111.70	$111.70	$111.70
Purchase #4	$94.38	4.191%	$98.3355	$98.34	$98.35	$98.30
Purchase #5	$101.76	7.829%	$109.7268	$109.73	$109.75	$109.70
Purchase #6	$130.94	13.117%	$148.1154	$148.12	$148.10	$148.10
Purchase #7	$114.40	13.384%	$129.7113	$129.71	$129.70	$129.70
7 purchase totals =	$715.65		$789.7674	$789.78	$789.80	$789.70