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	$39.97	12.154%	$44.828	$44.83	$44.85	$44.80
Purchase #2	$51.39	6.254%	$54.6039	$54.60	$54.60	$54.60
Purchase #3	$69.93	4.488%	$73.0685	$73.07	$73.05	$73.10
Purchase #4	$199.78	10.316%	$220.3893	$220.39	$220.40	$220.40
Purchase #5	$93.60	6.123%	$99.3311	$99.33	$99.35	$99.30
Purchase #6	$53.79	11.185%	$59.8064	$59.81	$59.80	$59.80
Purchase #7	$91.42	7.414%	$98.1979	$98.20	$98.20	$98.20
7 purchase totals =	$599.88		$650.2251	$650.23	$650.25	$650.20