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	$233.40	7.419%	$250.7159	$250.72	$250.70	$250.70
Purchase #2	$108.49	13.247%	$122.8617	$122.86	$122.85	$122.90
Purchase #3	$152.86	8.450%	$165.7767	$165.78	$165.80	$165.80
Purchase #4	$125.30	3.611%	$129.8246	$129.82	$129.80	$129.80
Purchase #5	$237.39	7.635%	$255.5147	$255.51	$255.50	$255.50
Purchase #6	$63.34	11.839%	$70.8388	$70.84	$70.85	$70.80
Purchase #7	$104.89	10.712%	$116.1258	$116.13	$116.15	$116.10
7 purchase totals =	$1,025.67		$1,111.6582	$1,111.66	$1,111.65	$1,111.60