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	$52.35	7.429%	$56.2391	$56.24	$56.25	$56.20
Purchase #2	$41.65	11.102%	$46.274	$46.27	$46.25	$46.30
Purchase #3	$73.72	9.830%	$80.9667	$80.97	$80.95	$81.00
Purchase #4	$192.31	4.327%	$200.6313	$200.63	$200.65	$200.60
Purchase #5	$98.61	11.450%	$109.9008	$109.90	$109.90	$109.90
Purchase #6	$86.66	5.813%	$91.6975	$91.70	$91.70	$91.70
Purchase #7	$49.99	6.300%	$53.1394	$53.14	$53.15	$53.10
7 purchase totals =	$595.29		$638.8488	$638.85	$638.85	$638.80