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	$143.34	3.628%	$148.5404	$148.54	$148.55	$148.50
Purchase #2	$57.49	9.511%	$62.9579	$62.96	$62.95	$63.00
Purchase #3	$71.91	10.559%	$79.503	$79.50	$79.50	$79.50
Purchase #4	$171.79	4.597%	$179.6872	$179.69	$179.70	$179.70
Purchase #5	$88.64	13.275%	$100.407	$100.41	$100.40	$100.40
Purchase #6	$18.76	12.482%	$21.1016	$21.10	$21.10	$21.10
Purchase #7	$29.71	12.138%	$33.3162	$33.32	$33.30	$33.30
7 purchase totals =	$581.64		$625.5133	$625.52	$625.50	$625.50