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	$45.88	7.413%	$49.2811	$49.28	$49.30	$49.30
Purchase #2	$66.86	9.429%	$73.1642	$73.16	$73.15	$73.20
Purchase #3	$109.44	12.406%	$123.0171	$123.02	$123.00	$123.00
Purchase #4	$133.91	10.537%	$148.0201	$148.02	$148.00	$148.00
Purchase #5	$77.78	8.527%	$84.4123	$84.41	$84.40	$84.40
Purchase #6	$64.27	13.393%	$72.8777	$72.88	$72.90	$72.90
Purchase #7	$168.90	7.259%	$181.1605	$181.16	$181.15	$181.20
7 purchase totals =	$667.04		$731.9330	$731.93	$731.90	$732.00