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	$86.90	9.175%	$94.8731	$94.87	$94.85	$94.90
Purchase #2	$42.38	7.322%	$45.4831	$45.48	$45.50	$45.50
Purchase #3	$178.55	5.121%	$187.6935	$187.69	$187.70	$187.70
Purchase #4	$214.86	13.343%	$243.5288	$243.53	$243.55	$243.50
Purchase #5	$48.41	4.602%	$50.6378	$50.64	$50.65	$50.60
Purchase #6	$96.61	12.502%	$108.6882	$108.69	$108.70	$108.70
Purchase #7	$102.90	8.761%	$111.9151	$111.92	$111.90	$111.90
7 purchase totals =	$770.61		$842.8196	$842.82	$842.85	$842.80