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	$227.37	12.347%	$255.4434	$255.44	$255.45	$255.40
Purchase #2	$151.62	10.415%	$167.4112	$167.41	$167.40	$167.40
Purchase #3	$131.34	4.354%	$137.0585	$137.06	$137.05	$137.10
Purchase #4	$165.29	11.158%	$183.7331	$183.73	$183.75	$183.70
Purchase #5	$58.29	9.759%	$63.9785	$63.98	$64.00	$64.00
Purchase #6	$112.64	12.204%	$126.3866	$126.39	$126.40	$126.40
Purchase #7	$90.77	6.398%	$96.5775	$96.58	$96.60	$96.60
7 purchase totals =	$937.32		$1,030.5888	$1,030.59	$1,030.65	$1,030.60