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	$212.79	5.155%	$223.7593	$223.76	$223.75	$223.80
Purchase #2	$131.40	13.439%	$149.0588	$149.06	$149.05	$149.10
Purchase #3	$77.70	9.602%	$85.1608	$85.16	$85.15	$85.20
Purchase #4	$105.54	6.449%	$112.3463	$112.35	$112.35	$112.30
Purchase #5	$85.94	3.697%	$89.1172	$89.12	$89.10	$89.10
Purchase #6	$62.28	10.438%	$68.7808	$68.78	$68.80	$68.80
Purchase #7	$80.94	5.143%	$85.1027	$85.10	$85.10	$85.10
7 purchase totals =	$756.59		$813.3259	$813.33	$813.30	$813.40