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	$225.93	11.233%	$251.3087	$251.31	$251.30	$251.30
Purchase #2	$81.68	5.644%	$86.29	$86.29	$86.30	$86.30
Purchase #3	$223.26	13.704%	$253.8556	$253.86	$253.85	$253.90
Purchase #4	$86.50	5.326%	$91.107	$91.11	$91.10	$91.10
Purchase #5	$168.97	3.404%	$174.7217	$174.72	$174.70	$174.70
Purchase #6	$180.65	6.192%	$191.8358	$191.84	$191.85	$191.80
Purchase #7	$142.89	13.631%	$162.3673	$162.37	$162.35	$162.40
7 purchase totals =	$1,109.88		$1,211.4861	$1,211.50	$1,211.45	$1,211.50