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	$120.51	9.441%	$131.8873	$131.89	$131.90	$131.90
Purchase #2	$187.65	4.326%	$195.7677	$195.77	$195.75	$195.80
Purchase #3	$34.30	11.254%	$38.1601	$38.16	$38.15	$38.20
Purchase #4	$184.58	7.519%	$198.4586	$198.46	$198.45	$198.50
Purchase #5	$19.74	10.363%	$21.7857	$21.79	$21.80	$21.80
Purchase #6	$231.39	10.382%	$255.4129	$255.41	$255.40	$255.40
Purchase #7	$91.61	10.279%	$101.0266	$101.03	$101.05	$101.00
7 purchase totals =	$869.78		$942.4989	$942.51	$942.50	$942.60