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	$229.58	5.353%	$241.8694	$241.87	$241.85	$241.90
Purchase #2	$65.90	12.696%	$74.2667	$74.27	$74.25	$74.30
Purchase #3	$81.72	9.139%	$89.1884	$89.19	$89.20	$89.20
Purchase #4	$45.50	10.398%	$50.2311	$50.23	$50.25	$50.20
Purchase #5	$191.80	4.482%	$200.3965	$200.40	$200.40	$200.40
Purchase #6	$213.71	13.351%	$242.2424	$242.24	$242.25	$242.20
Purchase #7	$73.77	12.247%	$82.8046	$82.80	$82.80	$82.80
7 purchase totals =	$901.98		$980.9991	$981.00	$981.00	$981.00