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	$67.80	5.389%	$71.4537	$71.45	$71.45	$71.50
Purchase #2	$87.84	8.735%	$95.5128	$95.51	$95.50	$95.50
Purchase #3	$78.92	12.455%	$88.7495	$88.75	$88.75	$88.70
Purchase #4	$173.30	5.337%	$182.549	$182.55	$182.55	$182.50
Purchase #5	$150.91	9.448%	$165.168	$165.17	$165.15	$165.20
Purchase #6	$26.82	12.809%	$30.2554	$30.26	$30.25	$30.30
Purchase #7	$31.62	8.455%	$34.2935	$34.29	$34.30	$34.30
7 purchase totals =	$617.21		$667.9819	$667.98	$667.95	$668.00