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	$209.59	8.692%	$227.8076	$227.81	$227.80	$227.80
Purchase #2	$203.88	5.534%	$215.1627	$215.16	$215.15	$215.20
Purchase #3	$211.27	10.338%	$233.1111	$233.11	$233.10	$233.10
Purchase #4	$53.63	5.256%	$56.4488	$56.45	$56.45	$56.40
Purchase #5	$152.88	12.751%	$172.3737	$172.37	$172.35	$172.40
Purchase #6	$250.45	7.733%	$269.8173	$269.82	$269.80	$269.80
Purchase #7	$39.76	13.627%	$45.1781	$45.18	$45.20	$45.20
7 purchase totals =	$1,121.46		$1,219.8993	$1,219.90	$1,219.85	$1,219.90