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	$38.25	10.448%	$42.2464	$42.25	$42.25	$42.20
Purchase #2	$79.26	11.794%	$88.6079	$88.61	$88.60	$88.60
Purchase #3	$41.72	11.837%	$46.6584	$46.66	$46.65	$46.70
Purchase #4	$94.91	5.692%	$100.3123	$100.31	$100.30	$100.30
Purchase #5	$102.93	6.300%	$109.4146	$109.41	$109.40	$109.40
Purchase #6	$143.76	13.873%	$163.7038	$163.70	$163.70	$163.70
Purchase #7	$46.34	9.807%	$50.8846	$50.88	$50.90	$50.90
7 purchase totals =	$547.17		$601.8280	$601.82	$601.80	$601.80