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	$12.83	5.554%	$13.5426	$13.54	$13.55	$13.50
Purchase #2	$153.28	11.812%	$171.3854	$171.39	$171.40	$171.40
Purchase #3	$148.51	9.525%	$162.6556	$162.66	$162.65	$162.70
Purchase #4	$56.56	5.691%	$59.7788	$59.78	$59.80	$59.80
Purchase #5	$185.40	10.738%	$205.3083	$205.31	$205.30	$205.30
Purchase #6	$90.25	12.309%	$101.3589	$101.36	$101.35	$101.40
Purchase #7	$234.84	6.170%	$249.3296	$249.33	$249.35	$249.30
7 purchase totals =	$881.67		$963.3592	$963.37	$963.40	$963.40