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	$180.96	4.600%	$189.2842	$189.28	$189.30	$189.30
Purchase #2	$87.84	3.160%	$90.6157	$90.62	$90.60	$90.60
Purchase #3	$234.60	10.616%	$259.5051	$259.51	$259.50	$259.50
Purchase #4	$58.27	12.554%	$65.5852	$65.59	$65.60	$65.60
Purchase #5	$245.54	8.797%	$267.1402	$267.14	$267.15	$267.10
Purchase #6	$49.67	8.818%	$54.0499	$54.05	$54.05	$54.00
Purchase #7	$39.73	8.688%	$43.1817	$43.18	$43.20	$43.20
7 purchase totals =	$896.61		$969.3620	$969.37	$969.40	$969.30