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	$228.69	6.358%	$243.2301	$243.23	$243.25	$243.20
Purchase #2	$33.32	12.339%	$37.4314	$37.43	$37.45	$37.40
Purchase #3	$80.69	6.328%	$85.7961	$85.80	$85.80	$85.80
Purchase #4	$197.79	4.539%	$206.7677	$206.77	$206.75	$206.80
Purchase #5	$96.92	3.726%	$100.5312	$100.53	$100.55	$100.50
Purchase #6	$64.77	8.770%	$70.4503	$70.45	$70.45	$70.50
Purchase #7	$96.28	5.139%	$101.2278	$101.23	$101.25	$101.20
7 purchase totals =	$798.46		$845.4346	$845.44	$845.50	$845.40