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	$83.53	9.477%	$91.4461	$91.45	$91.45	$91.40
Purchase #2	$49.64	11.265%	$55.2319	$55.23	$55.25	$55.20
Purchase #3	$123.98	7.204%	$132.9115	$132.91	$132.90	$132.90
Purchase #4	$145.89	12.121%	$163.5733	$163.57	$163.55	$163.60
Purchase #5	$150.63	9.213%	$164.5075	$164.51	$164.50	$164.50
Purchase #6	$27.45	13.165%	$31.0638	$31.06	$31.05	$31.10
Purchase #7	$149.25	11.152%	$165.8944	$165.89	$165.90	$165.90
7 purchase totals =	$730.37		$804.6285	$804.62	$804.60	$804.60