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	$249.36	3.821%	$258.888	$258.89	$258.90	$258.90
Purchase #2	$182.36	7.869%	$196.7099	$196.71	$196.70	$196.70
Purchase #3	$116.43	11.277%	$129.5598	$129.56	$129.55	$129.60
Purchase #4	$100.28	8.532%	$108.8359	$108.84	$108.85	$108.80
Purchase #5	$194.83	7.150%	$208.7603	$208.76	$208.75	$208.80
Purchase #6	$87.94	6.791%	$93.912	$93.91	$93.90	$93.90
Purchase #7	$18.82	10.562%	$20.8078	$20.81	$20.80	$20.80
7 purchase totals =	$950.02		$1,017.4737	$1,017.48	$1,017.45	$1,017.50