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	$53.59	12.658%	$60.3734	$60.37	$60.35	$60.40
Purchase #2	$31.27	5.776%	$33.0762	$33.08	$33.10	$33.10
Purchase #3	$49.59	7.830%	$53.4729	$53.47	$53.45	$53.50
Purchase #4	$121.57	5.835%	$128.6636	$128.66	$128.65	$128.70
Purchase #5	$36.37	3.276%	$37.5615	$37.56	$37.55	$37.60
Purchase #6	$105.39	4.306%	$109.9281	$109.93	$109.95	$109.90
Purchase #7	$5.43	10.212%	$5.9845	$5.98	$6.00	$6.00
7 purchase totals =	$403.21		$429.0602	$429.05	$429.05	$429.20