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	$185.57	9.600%	$203.3847	$203.38	$203.40	$203.40
Purchase #2	$62.66	6.233%	$66.5656	$66.57	$66.55	$66.60
Purchase #3	$152.41	8.853%	$165.9029	$165.90	$165.90	$165.90
Purchase #4	$145.25	6.752%	$155.0573	$155.06	$155.05	$155.10
Purchase #5	$97.26	11.243%	$108.1949	$108.19	$108.20	$108.20
Purchase #6	$50.72	13.220%	$57.4252	$57.43	$57.45	$57.40
Purchase #7	$232.86	6.203%	$247.3043	$247.30	$247.30	$247.30
7 purchase totals =	$926.73		$1,003.8349	$1,003.83	$1,003.85	$1,003.90