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	$133.74	12.494%	$150.4495	$150.45	$150.45	$150.40
Purchase #2	$79.76	13.148%	$90.2468	$90.25	$90.25	$90.20
Purchase #3	$164.74	9.730%	$180.7692	$180.77	$180.75	$180.80
Purchase #4	$40.78	11.861%	$45.6169	$45.62	$45.60	$45.60
Purchase #5	$12.88	10.355%	$14.2137	$14.21	$14.20	$14.20
Purchase #6	$38.71	9.134%	$42.2458	$42.25	$42.25	$42.20
Purchase #7	$182.73	9.724%	$200.4987	$200.50	$200.50	$200.50
7 purchase totals =	$653.34		$724.0406	$724.05	$724.00	$723.90