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	$47.30	6.733%	$50.4847	$50.48	$50.50	$50.50
Purchase #2	$222.56	9.307%	$243.2737	$243.27	$243.25	$243.30
Purchase #3	$78.26	9.254%	$85.5022	$85.50	$85.50	$85.50
Purchase #4	$153.49	3.537%	$158.9189	$158.92	$158.90	$158.90
Purchase #5	$43.88	4.297%	$45.7655	$45.77	$45.75	$45.80
Purchase #6	$113.89	9.306%	$124.4886	$124.49	$124.50	$124.50
Purchase #7	$183.28	6.736%	$195.6257	$195.63	$195.65	$195.60
7 purchase totals =	$842.66		$904.0593	$904.06	$904.05	$904.10