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	$125.71	9.797%	$138.0258	$138.03	$138.05	$138.00
Purchase #2	$41.89	4.799%	$43.9003	$43.90	$43.90	$43.90
Purchase #3	$42.38	8.622%	$46.034	$46.03	$46.05	$46.00
Purchase #4	$67.28	9.457%	$73.6427	$73.64	$73.65	$73.60
Purchase #5	$63.32	11.767%	$70.7709	$70.77	$70.75	$70.80
Purchase #6	$241.36	8.687%	$262.3269	$262.33	$262.35	$262.30
Purchase #7	$72.72	6.437%	$77.401	$77.40	$77.40	$77.40
7 purchase totals =	$654.66		$712.1016	$712.10	$712.15	$712.00