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	$86.88	4.116%	$90.456	$90.46	$90.45	$90.50
Purchase #2	$156.91	9.395%	$171.6517	$171.65	$171.65	$171.70
Purchase #3	$234.70	3.474%	$242.8535	$242.85	$242.85	$242.90
Purchase #4	$81.40	11.212%	$90.5266	$90.53	$90.55	$90.50
Purchase #5	$203.51	11.581%	$227.0785	$227.08	$227.10	$227.10
Purchase #6	$89.72	13.845%	$102.1417	$102.14	$102.15	$102.10
Purchase #7	$170.78	12.603%	$192.3034	$192.30	$192.30	$192.30
7 purchase totals =	$1,023.90		$1,117.0114	$1,117.01	$1,117.05	$1,117.10