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	$71.64	7.847%	$77.2616	$77.26	$77.25	$77.30
Purchase #2	$168.73	12.651%	$190.076	$190.08	$190.10	$190.10
Purchase #3	$174.26	4.602%	$182.2794	$182.28	$182.30	$182.30
Purchase #4	$113.89	10.323%	$125.6469	$125.65	$125.65	$125.60
Purchase #5	$228.61	11.725%	$255.4145	$255.41	$255.40	$255.40
Purchase #6	$27.36	9.139%	$29.8604	$29.86	$29.85	$29.90
Purchase #7	$67.79	5.610%	$71.593	$71.59	$71.60	$71.60
7 purchase totals =	$852.28		$932.1318	$932.13	$932.15	$932.20