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	$26.92	5.257%	$28.3352	$28.34	$28.35	$28.30
Purchase #2	$75.82	9.153%	$82.7598	$82.76	$82.75	$82.80
Purchase #3	$43.77	3.259%	$45.1965	$45.20	$45.20	$45.20
Purchase #4	$229.41	6.854%	$245.1338	$245.13	$245.15	$245.10
Purchase #5	$164.84	13.576%	$187.2187	$187.22	$187.20	$187.20
Purchase #6	$119.89	8.816%	$130.4595	$130.46	$130.45	$130.50
Purchase #7	$139.55	5.128%	$146.7061	$146.71	$146.70	$146.70
7 purchase totals =	$800.20		$865.8096	$865.82	$865.80	$865.80