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	$158.86	6.554%	$169.2717	$169.27	$169.25	$169.30
Purchase #2	$38.67	9.794%	$42.4573	$42.46	$42.45	$42.50
Purchase #3	$243.60	10.353%	$268.8199	$268.82	$268.80	$268.80
Purchase #4	$179.37	11.782%	$200.5034	$200.50	$200.50	$200.50
Purchase #5	$80.32	10.305%	$88.597	$88.60	$88.60	$88.60
Purchase #6	$175.89	11.104%	$195.4208	$195.42	$195.40	$195.40
Purchase #7	$9.36	8.503%	$10.1559	$10.16	$10.15	$10.20
7 purchase totals =	$886.07		$975.2260	$975.23	$975.15	$975.30