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	$171.41	12.670%	$193.1276	$193.13	$193.15	$193.10
Purchase #2	$133.30	4.737%	$139.6144	$139.61	$139.60	$139.60
Purchase #3	$53.94	8.134%	$58.3275	$58.33	$58.35	$58.30
Purchase #4	$93.86	4.474%	$98.0593	$98.06	$98.05	$98.10
Purchase #5	$102.68	3.147%	$105.9113	$105.91	$105.90	$105.90
Purchase #6	$153.82	5.732%	$162.637	$162.64	$162.65	$162.60
Purchase #7	$76.50	12.335%	$85.9363	$85.94	$85.95	$85.90
7 purchase totals =	$785.51		$843.6134	$843.62	$843.65	$843.50