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	$138.45	5.616%	$146.2254	$146.23	$146.25	$146.20
Purchase #2	$133.71	11.849%	$149.5533	$149.55	$149.55	$149.60
Purchase #3	$245.37	13.418%	$278.2937	$278.29	$278.30	$278.30
Purchase #4	$160.96	3.347%	$166.3473	$166.35	$166.35	$166.30
Purchase #5	$100.39	5.548%	$105.9596	$105.96	$105.95	$106.00
Purchase #6	$33.63	11.377%	$37.4561	$37.46	$37.45	$37.50
Purchase #7	$117.38	9.265%	$128.2553	$128.26	$128.25	$128.30
7 purchase totals =	$929.89		$1,012.0907	$1,012.10	$1,012.10	$1,012.20