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	$74.91	11.161%	$83.2707	$83.27	$83.25	$83.30
Purchase #2	$128.88	13.407%	$146.1589	$146.16	$146.15	$146.20
Purchase #3	$50.87	11.177%	$56.5557	$56.56	$56.55	$56.60
Purchase #4	$169.59	3.355%	$175.2797	$175.28	$175.30	$175.30
Purchase #5	$115.36	9.298%	$126.0862	$126.09	$126.10	$126.10
Purchase #6	$177.69	10.834%	$196.9409	$196.94	$196.95	$196.90
Purchase #7	$206.88	10.404%	$228.4038	$228.40	$228.40	$228.40
7 purchase totals =	$924.18		$1,012.6959	$1,012.70	$1,012.70	$1,012.80