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	$72.44	12.267%	$81.3262	$81.33	$81.35	$81.30
Purchase #2	$92.80	4.362%	$96.8479	$96.85	$96.85	$96.80
Purchase #3	$20.45	3.645%	$21.1954	$21.20	$21.20	$21.20
Purchase #4	$42.73	13.119%	$48.3357	$48.34	$48.35	$48.30
Purchase #5	$235.26	8.362%	$254.9324	$254.93	$254.95	$254.90
Purchase #6	$106.49	4.527%	$111.3108	$111.31	$111.30	$111.30
Purchase #7	$12.69	13.455%	$14.3974	$14.40	$14.40	$14.40
7 purchase totals =	$582.86		$628.3458	$628.36	$628.40	$628.20