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	$90.86	10.260%	$100.1822	$100.18	$100.20	$100.20
Purchase #2	$219.46	13.129%	$248.2729	$248.27	$248.25	$248.30
Purchase #3	$229.75	3.113%	$236.9021	$236.90	$236.90	$236.90
Purchase #4	$63.35	11.733%	$70.7829	$70.78	$70.80	$70.80
Purchase #5	$89.34	12.723%	$100.7067	$100.71	$100.70	$100.70
Purchase #6	$210.87	4.285%	$219.9058	$219.91	$219.90	$219.90
Purchase #7	$201.70	5.421%	$212.6342	$212.63	$212.65	$212.60
7 purchase totals =	$1,105.33		$1,189.3868	$1,189.38	$1,189.40	$1,189.40