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	$38.51	9.664%	$42.2316	$42.23	$42.25	$42.20
Purchase #2	$132.69	10.871%	$147.1147	$147.11	$147.10	$147.10
Purchase #3	$159.48	10.699%	$176.5428	$176.54	$176.55	$176.50
Purchase #4	$167.40	4.861%	$175.5373	$175.54	$175.55	$175.50
Purchase #5	$70.33	3.280%	$72.6368	$72.64	$72.65	$72.60
Purchase #6	$243.46	9.374%	$266.2819	$266.28	$266.30	$266.30
Purchase #7	$51.84	8.274%	$56.1292	$56.13	$56.15	$56.10
7 purchase totals =	$863.71		$936.4743	$936.47	$936.55	$936.30