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	$116.98	10.341%	$129.0769	$129.08	$129.10	$129.10
Purchase #2	$51.61	4.705%	$54.0383	$54.04	$54.05	$54.00
Purchase #3	$248.28	8.773%	$270.0616	$270.06	$270.05	$270.10
Purchase #4	$32.86	12.511%	$36.9711	$36.97	$36.95	$37.00
Purchase #5	$91.52	9.345%	$100.0725	$100.07	$100.05	$100.10
Purchase #6	$69.38	13.200%	$78.5382	$78.54	$78.55	$78.50
Purchase #7	$119.33	9.406%	$130.5542	$130.55	$130.55	$130.60
7 purchase totals =	$729.96		$799.3128	$799.31	$799.30	$799.40