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	$127.72	7.436%	$137.2173	$137.22	$137.20	$137.20
Purchase #2	$57.43	13.301%	$65.0688	$65.07	$65.05	$65.10
Purchase #3	$237.58	13.768%	$270.29	$270.29	$270.30	$270.30
Purchase #4	$71.45	9.207%	$78.0284	$78.03	$78.05	$78.00
Purchase #5	$145.49	3.391%	$150.4236	$150.42	$150.40	$150.40
Purchase #6	$136.27	4.774%	$142.7755	$142.78	$142.80	$142.80
Purchase #7	$37.80	9.418%	$41.36	$41.36	$41.35	$41.40
7 purchase totals =	$813.74		$885.1636	$885.17	$885.15	$885.20