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	$214.97	6.518%	$228.9817	$228.98	$229.00	$229.00
Purchase #2	$51.72	11.506%	$57.6709	$57.67	$57.65	$57.70
Purchase #3	$188.48	8.809%	$205.0832	$205.08	$205.10	$205.10
Purchase #4	$83.58	5.874%	$88.4895	$88.49	$88.50	$88.50
Purchase #5	$139.59	12.429%	$156.9396	$156.94	$156.95	$156.90
Purchase #6	$102.33	8.874%	$111.4108	$111.41	$111.40	$111.40
Purchase #7	$238.46	12.810%	$269.0067	$269.01	$269.00	$269.00
7 purchase totals =	$1,019.13		$1,117.5824	$1,117.58	$1,117.60	$1,117.60