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	$17.88	9.633%	$19.6024	$19.60	$19.60	$19.60
Purchase #2	$156.91	9.240%	$171.4085	$171.41	$171.40	$171.40
Purchase #3	$164.44	6.142%	$174.5399	$174.54	$174.55	$174.50
Purchase #4	$172.28	6.233%	$183.0182	$183.02	$183.00	$183.00
Purchase #5	$200.38	12.191%	$224.8083	$224.81	$224.80	$224.80
Purchase #6	$88.82	13.429%	$100.7476	$100.75	$100.75	$100.70
Purchase #7	$247.67	11.744%	$276.7564	$276.76	$276.75	$276.80
7 purchase totals =	$1,048.38		$1,150.8813	$1,150.89	$1,150.85	$1,150.80