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	$134.31	5.399%	$141.5614	$141.56	$141.55	$141.60
Purchase #2	$62.73	12.314%	$70.4546	$70.45	$70.45	$70.50
Purchase #3	$109.25	12.723%	$123.1499	$123.15	$123.15	$123.10
Purchase #4	$17.93	5.285%	$18.8776	$18.88	$18.90	$18.90
Purchase #5	$176.44	8.380%	$191.2257	$191.23	$191.25	$191.20
Purchase #6	$145.90	4.475%	$152.429	$152.43	$152.45	$152.40
Purchase #7	$49.29	5.734%	$52.1163	$52.12	$52.10	$52.10
7 purchase totals =	$695.85		$749.8145	$749.82	$749.85	$749.80