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	$84.65	6.815%	$90.4189	$90.42	$90.40	$90.40
Purchase #2	$125.67	9.334%	$137.4	$137.40	$137.40	$137.40
Purchase #3	$55.75	3.721%	$57.8245	$57.82	$57.80	$57.80
Purchase #4	$228.38	6.603%	$243.4599	$243.46	$243.45	$243.50
Purchase #5	$139.29	11.202%	$154.8933	$154.89	$154.90	$154.90
Purchase #6	$116.74	8.819%	$127.0353	$127.04	$127.05	$127.00
Purchase #7	$177.38	8.583%	$192.6045	$192.60	$192.60	$192.60
7 purchase totals =	$927.86		$1,003.6364	$1,003.63	$1,003.60	$1,003.60