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	$199.51	8.616%	$216.6998	$216.70	$216.70	$216.70
Purchase #2	$172.69	10.805%	$191.3492	$191.35	$191.35	$191.30
Purchase #3	$244.78	9.789%	$268.7415	$268.74	$268.75	$268.70
Purchase #4	$80.54	12.422%	$90.5447	$90.54	$90.55	$90.50
Purchase #5	$194.35	7.258%	$208.4559	$208.46	$208.45	$208.50
Purchase #6	$95.90	9.817%	$105.3145	$105.31	$105.30	$105.30
Purchase #7	$123.99	4.399%	$129.4443	$129.44	$129.45	$129.40
7 purchase totals =	$1,111.76		$1,210.5499	$1,210.54	$1,210.55	$1,210.40