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	$96.44	3.586%	$99.8983	$99.90	$99.90	$99.90
Purchase #2	$243.83	3.224%	$251.6911	$251.69	$251.70	$251.70
Purchase #3	$155.81	6.672%	$166.2056	$166.21	$166.20	$166.20
Purchase #4	$70.45	11.422%	$78.4968	$78.50	$78.50	$78.50
Purchase #5	$129.54	6.416%	$137.8513	$137.85	$137.85	$137.90
Purchase #6	$39.32	3.699%	$40.7744	$40.77	$40.75	$40.80
Purchase #7	$209.82	10.609%	$232.0798	$232.08	$232.10	$232.10
7 purchase totals =	$945.21		$1,006.9973	$1,007.00	$1,007.00	$1,007.10