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	$231.27	4.779%	$242.3224	$242.32	$242.30	$242.30
Purchase #2	$123.59	10.833%	$136.9785	$136.98	$137.00	$137.00
Purchase #3	$174.49	9.221%	$190.5797	$190.58	$190.60	$190.60
Purchase #4	$77.71	6.175%	$82.5086	$82.51	$82.50	$82.50
Purchase #5	$8.61	9.594%	$9.436	$9.44	$9.45	$9.40
Purchase #6	$169.26	9.661%	$185.6122	$185.61	$185.60	$185.60
Purchase #7	$219.58	12.859%	$247.8158	$247.82	$247.80	$247.80
7 purchase totals =	$1,004.51		$1,095.2532	$1,095.26	$1,095.25	$1,095.20