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	$75.53	9.840%	$82.9622	$82.96	$82.95	$83.00
Purchase #2	$236.56	9.310%	$258.5837	$258.58	$258.60	$258.60
Purchase #3	$229.78	11.343%	$255.8439	$255.84	$255.85	$255.80
Purchase #4	$80.39	3.794%	$83.44	$83.44	$83.45	$83.40
Purchase #5	$85.92	6.104%	$91.1646	$91.16	$91.15	$91.20
Purchase #6	$145.77	4.666%	$152.5716	$152.57	$152.55	$152.60
Purchase #7	$159.71	9.571%	$174.9958	$175.00	$175.00	$175.00
7 purchase totals =	$1,013.66		$1,099.5618	$1,099.55	$1,099.55	$1,099.60