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	$141.75	4.609%	$148.2833	$148.28	$148.30	$148.30
Purchase #2	$37.92	9.539%	$41.5372	$41.54	$41.55	$41.50
Purchase #3	$75.96	7.413%	$81.5909	$81.59	$81.60	$81.60
Purchase #4	$205.82	11.611%	$229.7178	$229.72	$229.70	$229.70
Purchase #5	$151.83	10.363%	$167.5641	$167.56	$167.55	$167.60
Purchase #6	$48.85	4.844%	$51.2163	$51.22	$51.20	$51.20
Purchase #7	$57.47	3.389%	$59.4177	$59.42	$59.40	$59.40
7 purchase totals =	$719.60		$779.3273	$779.33	$779.30	$779.30