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	$37.35	6.456%	$39.7613	$39.76	$39.75	$39.80
Purchase #2	$93.76	5.874%	$99.2675	$99.27	$99.25	$99.30
Purchase #3	$134.79	8.773%	$146.6151	$146.62	$146.60	$146.60
Purchase #4	$198.40	13.376%	$224.938	$224.94	$224.95	$224.90
Purchase #5	$23.97	7.164%	$25.6872	$25.69	$25.70	$25.70
Purchase #6	$163.91	5.474%	$172.8824	$172.88	$172.90	$172.90
Purchase #7	$63.93	11.521%	$71.2954	$71.30	$71.30	$71.30
7 purchase totals =	$716.11		$780.4469	$780.46	$780.45	$780.50