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	$80.54	3.200%	$83.1173	$83.12	$83.10	$83.10
Purchase #2	$61.90	8.717%	$67.2958	$67.30	$67.30	$67.30
Purchase #3	$184.50	6.662%	$196.7914	$196.79	$196.80	$196.80
Purchase #4	$145.39	6.270%	$154.506	$154.51	$154.50	$154.50
Purchase #5	$55.75	10.658%	$61.6918	$61.69	$61.70	$61.70
Purchase #6	$68.45	7.472%	$73.5646	$73.56	$73.55	$73.60
Purchase #7	$129.65	6.694%	$138.3288	$138.33	$138.35	$138.30
7 purchase totals =	$726.18		$775.2957	$775.30	$775.30	$775.30