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	$129.74	5.434%	$136.7901	$136.79	$136.80	$136.80
Purchase #2	$133.69	6.860%	$142.8611	$142.86	$142.85	$142.90
Purchase #3	$19.73	8.218%	$21.3514	$21.35	$21.35	$21.40
Purchase #4	$22.48	7.116%	$24.0797	$24.08	$24.10	$24.10
Purchase #5	$225.54	6.476%	$240.146	$240.15	$240.15	$240.10
Purchase #6	$141.60	12.560%	$159.385	$159.39	$159.40	$159.40
Purchase #7	$222.91	9.861%	$244.8912	$244.89	$244.90	$244.90
7 purchase totals =	$895.69		$969.5045	$969.51	$969.55	$969.60