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	$224.85	8.773%	$244.5761	$244.58	$244.60	$244.60
Purchase #2	$67.64	12.753%	$76.2661	$76.27	$76.25	$76.30
Purchase #3	$213.85	13.809%	$243.3805	$243.38	$243.40	$243.40
Purchase #4	$70.33	11.469%	$78.3961	$78.40	$78.40	$78.40
Purchase #5	$98.61	8.652%	$107.1417	$107.14	$107.15	$107.10
Purchase #6	$80.55	10.328%	$88.8692	$88.87	$88.85	$88.90
Purchase #7	$147.63	11.478%	$164.575	$164.58	$164.60	$164.60
7 purchase totals =	$903.46		$1,003.2047	$1,003.22	$1,003.25	$1,003.30