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	$39.65	3.809%	$41.1603	$41.16	$41.15	$41.20
Purchase #2	$39.36	4.870%	$41.2768	$41.28	$41.30	$41.30
Purchase #3	$33.56	11.801%	$37.5204	$37.52	$37.50	$37.50
Purchase #4	$58.95	7.406%	$63.3158	$63.32	$63.30	$63.30
Purchase #5	$190.95	9.510%	$209.1093	$209.11	$209.10	$209.10
Purchase #6	$67.50	13.650%	$76.7138	$76.71	$76.70	$76.70
Purchase #7	$170.91	13.828%	$194.5434	$194.54	$194.55	$194.50
7 purchase totals =	$600.88		$663.6398	$663.64	$663.60	$663.60