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	$164.46	11.501%	$183.3745	$183.37	$183.35	$183.40
Purchase #2	$99.77	4.174%	$103.9344	$103.93	$103.95	$103.90
Purchase #3	$237.84	10.508%	$262.8322	$262.83	$262.85	$262.80
Purchase #4	$230.60	4.223%	$240.3382	$240.34	$240.35	$240.30
Purchase #5	$124.69	4.190%	$129.9145	$129.91	$129.90	$129.90
Purchase #6	$63.34	13.715%	$72.0271	$72.03	$72.05	$72.00
Purchase #7	$47.62	6.515%	$50.7224	$50.72	$50.70	$50.70
7 purchase totals =	$968.32		$1,043.1433	$1,043.13	$1,043.15	$1,043.00