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	$110.83	3.551%	$114.7656	$114.77	$114.75	$114.80
Purchase #2	$72.47	8.340%	$78.514	$78.51	$78.50	$78.50
Purchase #3	$66.88	5.787%	$70.7503	$70.75	$70.75	$70.80
Purchase #4	$71.41	11.644%	$79.725	$79.73	$79.75	$79.70
Purchase #5	$99.96	3.705%	$103.6635	$103.66	$103.65	$103.70
Purchase #6	$228.54	10.818%	$253.2635	$253.26	$253.25	$253.30
Purchase #7	$134.94	3.326%	$139.4281	$139.43	$139.45	$139.40
7 purchase totals =	$785.03		$840.1100	$840.11	$840.10	$840.20