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	$94.55	4.622%	$98.9201	$98.92	$98.90	$98.90
Purchase #2	$71.33	7.173%	$76.4465	$76.45	$76.45	$76.40
Purchase #3	$185.48	10.392%	$204.7551	$204.76	$204.75	$204.80
Purchase #4	$230.89	13.130%	$261.2059	$261.21	$261.20	$261.20
Purchase #5	$45.29	11.476%	$50.4875	$50.49	$50.50	$50.50
Purchase #6	$74.27	6.290%	$78.9416	$78.94	$78.95	$78.90
Purchase #7	$43.66	12.756%	$49.2293	$49.23	$49.25	$49.20
7 purchase totals =	$745.47		$819.9860	$820.00	$820.00	$819.90