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	$49.79	4.783%	$52.1715	$52.17	$52.15	$52.20
Purchase #2	$63.70	12.214%	$71.4803	$71.48	$71.50	$71.50
Purchase #3	$137.85	13.841%	$156.9298	$156.93	$156.95	$156.90
Purchase #4	$155.53	6.284%	$165.3035	$165.30	$165.30	$165.30
Purchase #5	$58.51	5.321%	$61.6233	$61.62	$61.60	$61.60
Purchase #6	$12.73	4.372%	$13.2866	$13.29	$13.30	$13.30
Purchase #7	$235.56	9.692%	$258.3905	$258.39	$258.40	$258.40
7 purchase totals =	$713.67		$779.1855	$779.18	$779.20	$779.20