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	$161.55	13.787%	$183.8229	$183.82	$183.80	$183.80
Purchase #2	$61.64	4.583%	$64.465	$64.47	$64.45	$64.50
Purchase #3	$164.99	8.760%	$179.4431	$179.44	$179.45	$179.40
Purchase #4	$119.52	10.774%	$132.3971	$132.40	$132.40	$132.40
Purchase #5	$171.66	11.332%	$191.1125	$191.11	$191.10	$191.10
Purchase #6	$62.86	13.625%	$71.4247	$71.42	$71.40	$71.40
Purchase #7	$11.43	5.510%	$12.0598	$12.06	$12.05	$12.10
7 purchase totals =	$753.65		$834.7251	$834.72	$834.65	$834.70