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	$229.77	8.805%	$250.0012	$250.00	$250.00	$250.00
Purchase #2	$94.75	10.227%	$104.4401	$104.44	$104.45	$104.40
Purchase #3	$78.80	8.362%	$85.3893	$85.39	$85.40	$85.40
Purchase #4	$161.71	13.670%	$183.8158	$183.82	$183.80	$183.80
Purchase #5	$80.82	13.711%	$91.9012	$91.90	$91.90	$91.90
Purchase #6	$118.91	10.600%	$131.5145	$131.51	$131.50	$131.50
Purchase #7	$187.53	5.730%	$198.2755	$198.28	$198.30	$198.30
7 purchase totals =	$952.29		$1,045.3376	$1,045.34	$1,045.35	$1,045.30