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	$82.94	8.854%	$90.2835	$90.28	$90.30	$90.30
Purchase #2	$219.27	8.311%	$237.4935	$237.49	$237.50	$237.50
Purchase #3	$194.76	13.660%	$221.3642	$221.36	$221.35	$221.40
Purchase #4	$250.49	8.872%	$272.7135	$272.71	$272.70	$272.70
Purchase #5	$139.42	8.702%	$151.5523	$151.55	$151.55	$151.60
Purchase #6	$78.58	12.341%	$88.2776	$88.28	$88.30	$88.30
Purchase #7	$134.76	5.483%	$142.1489	$142.15	$142.15	$142.10
7 purchase totals =	$1,100.22		$1,203.8335	$1,203.82	$1,203.85	$1,203.90