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	$73.44	6.620%	$78.3017	$78.30	$78.30	$78.30
Purchase #2	$248.90	4.373%	$259.7844	$259.78	$259.80	$259.80
Purchase #3	$83.29	6.680%	$88.8538	$88.85	$88.85	$88.90
Purchase #4	$140.64	9.405%	$153.8672	$153.87	$153.85	$153.90
Purchase #5	$88.67	3.166%	$91.4773	$91.48	$91.50	$91.50
Purchase #6	$208.32	10.368%	$229.9186	$229.92	$229.90	$229.90
Purchase #7	$234.72	9.573%	$257.1897	$257.19	$257.20	$257.20
7 purchase totals =	$1,077.98		$1,159.3927	$1,159.39	$1,159.40	$1,159.50