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	$110.52	10.729%	$122.3777	$122.38	$122.40	$122.40
Purchase #2	$76.46	7.630%	$82.2939	$82.29	$82.30	$82.30
Purchase #3	$94.86	3.563%	$98.2399	$98.24	$98.25	$98.20
Purchase #4	$26.37	12.263%	$29.6038	$29.60	$29.60	$29.60
Purchase #5	$27.45	5.148%	$28.8631	$28.86	$28.85	$28.90
Purchase #6	$78.46	4.397%	$81.9099	$81.91	$81.90	$81.90
Purchase #7	$118.40	10.642%	$131.0001	$131.00	$131.00	$131.00
7 purchase totals =	$532.52		$574.2884	$574.28	$574.30	$574.30