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	$131.85	6.755%	$140.7565	$140.76	$140.75	$140.80
Purchase #2	$124.54	6.305%	$132.3922	$132.39	$132.40	$132.40
Purchase #3	$17.89	9.589%	$19.6055	$19.61	$19.60	$19.60
Purchase #4	$40.34	5.274%	$42.4675	$42.47	$42.45	$42.50
Purchase #5	$37.94	6.501%	$40.4065	$40.41	$40.40	$40.40
Purchase #6	$106.48	8.148%	$115.156	$115.16	$115.15	$115.20
Purchase #7	$71.71	4.672%	$75.0603	$75.06	$75.05	$75.10
7 purchase totals =	$530.75		$565.8445	$565.86	$565.80	$566.00