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	$225.49	3.454%	$233.2784	$233.28	$233.30	$233.30
Purchase #2	$102.77	5.656%	$108.5827	$108.58	$108.60	$108.60
Purchase #3	$61.83	8.506%	$67.0893	$67.09	$67.10	$67.10
Purchase #4	$67.33	10.289%	$74.2576	$74.26	$74.25	$74.30
Purchase #5	$67.36	7.384%	$72.3339	$72.33	$72.35	$72.30
Purchase #6	$249.58	6.512%	$265.8326	$265.83	$265.85	$265.80
Purchase #7	$167.25	6.644%	$178.3621	$178.36	$178.35	$178.40
7 purchase totals =	$941.61		$999.7366	$999.73	$999.80	$999.80