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	$84.34	7.108%	$90.3349	$90.33	$90.35	$90.30
Purchase #2	$20.47	6.216%	$21.7424	$21.74	$21.75	$21.70
Purchase #3	$218.55	13.476%	$248.0018	$248.00	$248.00	$248.00
Purchase #4	$155.97	10.775%	$172.7758	$172.78	$172.80	$172.80
Purchase #5	$17.64	6.274%	$18.7467	$18.75	$18.75	$18.70
Purchase #6	$131.34	8.496%	$142.4986	$142.50	$142.50	$142.50
Purchase #7	$203.47	12.631%	$229.1703	$229.17	$229.15	$229.20
7 purchase totals =	$831.78		$923.2705	$923.27	$923.30	$923.20