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	$88.54	12.131%	$99.2808	$99.28	$99.30	$99.30
Purchase #2	$72.66	6.128%	$77.1126	$77.11	$77.10	$77.10
Purchase #3	$132.41	9.287%	$144.7069	$144.71	$144.70	$144.70
Purchase #4	$233.70	9.280%	$255.3874	$255.39	$255.40	$255.40
Purchase #5	$98.59	3.369%	$101.9115	$101.91	$101.90	$101.90
Purchase #6	$234.49	6.728%	$250.2665	$250.27	$250.25	$250.30
Purchase #7	$17.53	13.647%	$19.9223	$19.92	$19.90	$19.90
7 purchase totals =	$877.92		$948.5880	$948.59	$948.55	$948.60