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	$29.33	3.575%	$30.3785	$30.38	$30.40	$30.40
Purchase #2	$195.63	12.121%	$219.3423	$219.34	$219.35	$219.30
Purchase #3	$217.98	4.697%	$228.2185	$228.22	$228.20	$228.20
Purchase #4	$180.57	8.697%	$196.2742	$196.27	$196.25	$196.30
Purchase #5	$28.31	8.128%	$30.611	$30.61	$30.60	$30.60
Purchase #6	$55.81	3.767%	$57.9124	$57.91	$57.90	$57.90
Purchase #7	$248.76	12.329%	$279.4296	$279.43	$279.45	$279.40
7 purchase totals =	$956.39		$1,042.1665	$1,042.16	$1,042.15	$1,042.10