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	$201.37	3.741%	$208.9033	$208.90	$208.90	$208.90
Purchase #2	$64.55	11.369%	$71.8887	$71.89	$71.90	$71.90
Purchase #3	$119.42	11.414%	$133.0506	$133.05	$133.05	$133.10
Purchase #4	$81.31	11.717%	$90.8371	$90.84	$90.85	$90.80
Purchase #5	$65.67	12.706%	$74.014	$74.01	$74.00	$74.00
Purchase #6	$141.78	7.378%	$152.2405	$152.24	$152.25	$152.20
Purchase #7	$105.58	11.839%	$118.0796	$118.08	$118.10	$118.10
7 purchase totals =	$779.68		$849.0138	$849.01	$849.05	$849.00