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	$90.74	8.291%	$98.2633	$98.26	$98.25	$98.30
Purchase #2	$139.71	10.312%	$154.1169	$154.12	$154.10	$154.10
Purchase #3	$66.28	7.863%	$71.4916	$71.49	$71.50	$71.50
Purchase #4	$81.48	5.310%	$85.8066	$85.81	$85.80	$85.80
Purchase #5	$25.61	10.697%	$28.3495	$28.35	$28.35	$28.30
Purchase #6	$39.26	11.387%	$43.7305	$43.73	$43.75	$43.70
Purchase #7	$80.39	12.513%	$90.4492	$90.45	$90.45	$90.40
7 purchase totals =	$523.47		$572.2076	$572.21	$572.20	$572.10