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	$77.83	5.756%	$82.3099	$82.31	$82.30	$82.30
Purchase #2	$53.48	11.341%	$59.5452	$59.55	$59.55	$59.50
Purchase #3	$70.71	12.841%	$79.7899	$79.79	$79.80	$79.80
Purchase #4	$159.48	10.199%	$175.7454	$175.75	$175.75	$175.70
Purchase #5	$214.67	11.169%	$238.6465	$238.65	$238.65	$238.60
Purchase #6	$80.39	12.555%	$90.483	$90.48	$90.50	$90.50
Purchase #7	$110.43	12.427%	$124.1531	$124.15	$124.15	$124.20
7 purchase totals =	$766.99		$850.6730	$850.68	$850.70	$850.60