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	$100.32	3.649%	$103.9807	$103.98	$104.00	$104.00
Purchase #2	$75.52	9.110%	$82.3999	$82.40	$82.40	$82.40
Purchase #3	$98.59	12.339%	$110.755	$110.76	$110.75	$110.80
Purchase #4	$100.90	12.267%	$113.2774	$113.28	$113.30	$113.30
Purchase #5	$107.71	9.689%	$118.146	$118.15	$118.15	$118.10
Purchase #6	$33.62	10.237%	$37.0617	$37.06	$37.05	$37.10
Purchase #7	$223.28	8.443%	$242.1315	$242.13	$242.15	$242.10
7 purchase totals =	$739.94		$807.7522	$807.76	$807.80	$807.80