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	$166.29	7.724%	$179.1342	$179.13	$179.15	$179.10
Purchase #2	$129.59	13.660%	$147.292	$147.29	$147.30	$147.30
Purchase #3	$72.98	12.752%	$82.2864	$82.29	$82.30	$82.30
Purchase #4	$214.70	11.115%	$238.5639	$238.56	$238.55	$238.60
Purchase #5	$202.83	3.599%	$210.1299	$210.13	$210.15	$210.10
Purchase #6	$172.32	10.688%	$190.7376	$190.74	$190.75	$190.70
Purchase #7	$188.27	5.322%	$198.2897	$198.29	$198.30	$198.30
7 purchase totals =	$1,146.98		$1,246.4337	$1,246.43	$1,246.50	$1,246.40