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	$38.75	6.342%	$41.2075	$41.21	$41.20	$41.20
Purchase #2	$110.95	11.729%	$123.9633	$123.96	$123.95	$124.00
Purchase #3	$137.69	7.816%	$148.4519	$148.45	$148.45	$148.50
Purchase #4	$55.37	8.269%	$59.9485	$59.95	$59.95	$59.90
Purchase #5	$230.37	6.248%	$244.7635	$244.76	$244.75	$244.80
Purchase #6	$38.60	9.497%	$42.2658	$42.27	$42.25	$42.30
Purchase #7	$134.47	7.639%	$144.7422	$144.74	$144.75	$144.70
7 purchase totals =	$746.20		$805.3427	$805.34	$805.30	$805.40