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	$14.27	13.150%	$16.1465	$16.15	$16.15	$16.10
Purchase #2	$250.69	12.708%	$282.5477	$282.55	$282.55	$282.50
Purchase #3	$73.28	6.109%	$77.7567	$77.76	$77.75	$77.80
Purchase #4	$82.82	11.411%	$92.2706	$92.27	$92.25	$92.30
Purchase #5	$78.99	8.707%	$85.8677	$85.87	$85.85	$85.90
Purchase #6	$46.61	12.629%	$52.4964	$52.50	$52.50	$52.50
Purchase #7	$60.76	6.134%	$64.487	$64.49	$64.50	$64.50
7 purchase totals =	$607.42		$671.5726	$671.59	$671.55	$671.60