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	$51.44	10.778%	$56.9842	$56.98	$57.00	$57.00
Purchase #2	$40.86	11.606%	$45.6022	$45.60	$45.60	$45.60
Purchase #3	$33.85	9.672%	$37.124	$37.12	$37.10	$37.10
Purchase #4	$170.90	12.267%	$191.8643	$191.86	$191.85	$191.90
Purchase #5	$190.75	10.765%	$211.2842	$211.28	$211.30	$211.30
Purchase #6	$61.62	7.171%	$66.0388	$66.04	$66.05	$66.00
Purchase #7	$139.72	3.434%	$144.518	$144.52	$144.50	$144.50
7 purchase totals =	$689.14		$753.4157	$753.40	$753.40	$753.40