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	$112.81	4.485%	$117.8695	$117.87	$117.85	$117.90
Purchase #2	$50.44	10.782%	$55.8784	$55.88	$55.90	$55.90
Purchase #3	$38.51	10.168%	$42.4257	$42.43	$42.45	$42.40
Purchase #4	$55.88	11.833%	$62.4923	$62.49	$62.50	$62.50
Purchase #5	$31.98	6.753%	$34.1396	$34.14	$34.15	$34.10
Purchase #6	$48.55	13.332%	$55.0227	$55.02	$55.00	$55.00
Purchase #7	$136.44	6.649%	$145.5119	$145.51	$145.50	$145.50
7 purchase totals =	$474.61		$513.3401	$513.34	$513.35	$513.30