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	$82.87	8.169%	$89.6397	$89.64	$89.65	$89.60
Purchase #2	$207.45	7.488%	$222.9839	$222.98	$223.00	$223.00
Purchase #3	$189.71	12.483%	$213.3915	$213.39	$213.40	$213.40
Purchase #4	$14.29	11.620%	$15.9505	$15.95	$15.95	$16.00
Purchase #5	$172.56	7.396%	$185.3225	$185.32	$185.30	$185.30
Purchase #6	$108.78	6.391%	$115.7321	$115.73	$115.75	$115.70
Purchase #7	$13.61	12.501%	$15.3114	$15.31	$15.30	$15.30
7 purchase totals =	$789.27		$858.3316	$858.32	$858.35	$858.30