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	$28.42	10.771%	$31.4811	$31.48	$31.50	$31.50
Purchase #2	$31.63	13.549%	$35.9155	$35.92	$35.90	$35.90
Purchase #3	$236.94	9.786%	$260.1269	$260.13	$260.15	$260.10
Purchase #4	$135.59	6.529%	$144.4427	$144.44	$144.45	$144.40
Purchase #5	$65.27	10.817%	$72.3303	$72.33	$72.35	$72.30
Purchase #6	$10.54	12.350%	$11.8417	$11.84	$11.85	$11.80
Purchase #7	$13.46	9.627%	$14.7558	$14.76	$14.75	$14.80
7 purchase totals =	$521.85		$570.8940	$570.90	$570.95	$570.80