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	$131.45	13.782%	$149.5664	$149.57	$149.55	$149.60
Purchase #2	$15.89	10.592%	$17.5731	$17.57	$17.55	$17.60
Purchase #3	$226.97	13.683%	$258.0263	$258.03	$258.05	$258.00
Purchase #4	$151.83	5.261%	$159.8178	$159.82	$159.80	$159.80
Purchase #5	$37.59	13.855%	$42.7981	$42.80	$42.80	$42.80
Purchase #6	$79.56	7.832%	$85.7911	$85.79	$85.80	$85.80
Purchase #7	$89.48	3.185%	$92.3299	$92.33	$92.35	$92.30
7 purchase totals =	$732.77		$805.9027	$805.91	$805.90	$805.90