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	$244.67	12.756%	$275.8801	$275.88	$275.90	$275.90
Purchase #2	$181.51	10.561%	$200.6793	$200.68	$200.70	$200.70
Purchase #3	$58.85	13.658%	$66.8877	$66.89	$66.90	$66.90
Purchase #4	$159.86	6.628%	$170.4555	$170.46	$170.45	$170.50
Purchase #5	$120.85	8.520%	$131.1464	$131.15	$131.15	$131.10
Purchase #6	$171.92	11.600%	$191.8627	$191.86	$191.85	$191.90
Purchase #7	$78.46	8.128%	$84.8372	$84.84	$84.85	$84.80
7 purchase totals =	$1,016.12		$1,121.7489	$1,121.76	$1,121.80	$1,121.80