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	$108.60	10.452%	$119.9509	$119.95	$119.95	$120.00
Purchase #2	$76.37	7.568%	$82.1497	$82.15	$82.15	$82.10
Purchase #3	$80.43	12.422%	$90.421	$90.42	$90.40	$90.40
Purchase #4	$45.58	11.431%	$50.7902	$50.79	$50.80	$50.80
Purchase #5	$193.38	3.614%	$200.3688	$200.37	$200.35	$200.40
Purchase #6	$164.25	7.840%	$177.1272	$177.13	$177.15	$177.10
Purchase #7	$116.44	10.608%	$128.792	$128.79	$128.80	$128.80
7 purchase totals =	$785.05		$849.5998	$849.60	$849.60	$849.60