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	$116.86	4.539%	$122.1643	$122.16	$122.15	$122.20
Purchase #2	$92.85	4.314%	$96.8555	$96.86	$96.85	$96.90
Purchase #3	$111.44	7.738%	$120.0632	$120.06	$120.05	$120.10
Purchase #4	$36.29	3.766%	$37.6567	$37.66	$37.65	$37.70
Purchase #5	$80.81	12.275%	$90.7294	$90.73	$90.75	$90.70
Purchase #6	$71.34	13.279%	$80.8132	$80.81	$80.80	$80.80
Purchase #7	$49.58	4.681%	$51.9008	$51.90	$51.90	$51.90
7 purchase totals =	$559.17		$600.1831	$600.18	$600.15	$600.30