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	$26.31	3.141%	$27.1364	$27.14	$27.15	$27.10
Purchase #2	$243.38	10.666%	$269.3389	$269.34	$269.35	$269.30
Purchase #3	$92.25	13.451%	$104.6585	$104.66	$104.65	$104.70
Purchase #4	$249.84	12.316%	$280.6103	$280.61	$280.60	$280.60
Purchase #5	$218.86	11.167%	$243.3001	$243.30	$243.30	$243.30
Purchase #6	$112.29	13.526%	$127.4783	$127.48	$127.50	$127.50
Purchase #7	$181.33	5.615%	$191.5117	$191.51	$191.50	$191.50
7 purchase totals =	$1,124.26		$1,244.0342	$1,244.04	$1,244.05	$1,244.00