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	$173.98	8.449%	$188.6796	$188.68	$188.70	$188.70
Purchase #2	$99.27	5.549%	$104.7785	$104.78	$104.80	$104.80
Purchase #3	$160.89	6.119%	$170.7349	$170.73	$170.75	$170.70
Purchase #4	$53.28	11.357%	$59.331	$59.33	$59.35	$59.30
Purchase #5	$73.50	10.742%	$81.3954	$81.40	$81.40	$81.40
Purchase #6	$79.32	11.486%	$88.4307	$88.43	$88.45	$88.40
Purchase #7	$38.92	4.776%	$40.7788	$40.78	$40.80	$40.80
7 purchase totals =	$679.16		$734.1289	$734.13	$734.25	$734.10