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	$156.56	4.787%	$164.0545	$164.05	$164.05	$164.10
Purchase #2	$86.61	5.758%	$91.597	$91.60	$91.60	$91.60
Purchase #3	$9.46	12.799%	$10.6708	$10.67	$10.65	$10.70
Purchase #4	$127.93	9.601%	$140.2126	$140.21	$140.20	$140.20
Purchase #5	$45.97	9.387%	$50.2852	$50.29	$50.30	$50.30
Purchase #6	$249.42	8.590%	$270.8452	$270.85	$270.85	$270.80
Purchase #7	$129.82	9.817%	$142.5644	$142.56	$142.55	$142.60
7 purchase totals =	$805.77		$870.2297	$870.23	$870.20	$870.30