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	$37.27	8.339%	$40.3779	$40.38	$40.40	$40.40
Purchase #2	$131.86	3.869%	$136.9617	$136.96	$136.95	$137.00
Purchase #3	$53.93	7.792%	$58.1322	$58.13	$58.15	$58.10
Purchase #4	$99.96	13.410%	$113.3646	$113.36	$113.35	$113.40
Purchase #5	$186.43	10.660%	$206.3034	$206.30	$206.30	$206.30
Purchase #6	$159.95	7.822%	$172.4613	$172.46	$172.45	$172.50
Purchase #7	$116.44	9.281%	$127.2468	$127.25	$127.25	$127.20
7 purchase totals =	$785.84		$854.8479	$854.84	$854.85	$854.90