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	$52.77	3.232%	$54.4755	$54.48	$54.50	$54.50
Purchase #2	$133.96	13.176%	$151.6106	$151.61	$151.60	$151.60
Purchase #3	$142.63	8.470%	$154.7108	$154.71	$154.70	$154.70
Purchase #4	$123.28	6.414%	$131.1872	$131.19	$131.20	$131.20
Purchase #5	$95.65	3.173%	$98.685	$98.69	$98.70	$98.70
Purchase #6	$79.26	12.683%	$89.3125	$89.31	$89.30	$89.30
Purchase #7	$213.63	9.344%	$233.5916	$233.59	$233.60	$233.60
7 purchase totals =	$841.18		$913.5732	$913.58	$913.60	$913.60