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	$69.46	7.799%	$74.8772	$74.88	$74.90	$74.90
Purchase #2	$63.75	11.777%	$71.2578	$71.26	$71.25	$71.30
Purchase #3	$63.47	6.411%	$67.5391	$67.54	$67.55	$67.50
Purchase #4	$101.84	7.325%	$109.2998	$109.30	$109.30	$109.30
Purchase #5	$148.92	12.249%	$167.1612	$167.16	$167.15	$167.20
Purchase #6	$243.29	11.628%	$271.5798	$271.58	$271.60	$271.60
Purchase #7	$55.54	7.449%	$59.6772	$59.68	$59.70	$59.70
7 purchase totals =	$746.27		$821.3921	$821.40	$821.45	$821.50