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	$221.32	3.123%	$228.2318	$228.23	$228.25	$228.20
Purchase #2	$89.51	12.514%	$100.7113	$100.71	$100.70	$100.70
Purchase #3	$165.54	7.696%	$178.28	$178.28	$178.30	$178.30
Purchase #4	$25.80	3.752%	$26.768	$26.77	$26.75	$26.80
Purchase #5	$31.72	3.621%	$32.8686	$32.87	$32.85	$32.90
Purchase #6	$161.52	9.873%	$177.4669	$177.47	$177.45	$177.50
Purchase #7	$83.31	7.238%	$89.34	$89.34	$89.35	$89.30
7 purchase totals =	$778.72		$833.6666	$833.67	$833.65	$833.70