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	$82.56	9.152%	$90.1159	$90.12	$90.10	$90.10
Purchase #2	$103.39	10.112%	$113.8448	$113.84	$113.85	$113.80
Purchase #3	$123.99	3.107%	$127.8424	$127.84	$127.85	$127.80
Purchase #4	$235.55	12.350%	$264.6404	$264.64	$264.65	$264.60
Purchase #5	$28.72	11.262%	$31.9544	$31.95	$31.95	$32.00
Purchase #6	$204.93	11.634%	$228.7716	$228.77	$228.75	$228.80
Purchase #7	$12.91	10.863%	$14.3124	$14.31	$14.30	$14.30
7 purchase totals =	$792.05		$871.4819	$871.47	$871.45	$871.40