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	$248.97	13.467%	$282.4988	$282.50	$282.50	$282.50
Purchase #2	$42.56	9.417%	$46.5679	$46.57	$46.55	$46.60
Purchase #3	$62.49	10.519%	$69.0633	$69.06	$69.05	$69.10
Purchase #4	$230.29	7.632%	$247.8657	$247.87	$247.85	$247.90
Purchase #5	$141.51	11.153%	$157.2926	$157.29	$157.30	$157.30
Purchase #6	$193.55	11.377%	$215.5702	$215.57	$215.55	$215.60
Purchase #7	$82.96	9.395%	$90.7541	$90.75	$90.75	$90.80
7 purchase totals =	$1,002.33		$1,109.6126	$1,109.61	$1,109.55	$1,109.80