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	$250.54	6.741%	$267.4289	$267.43	$267.45	$267.40
Purchase #2	$51.40	4.318%	$53.6195	$53.62	$53.60	$53.60
Purchase #3	$150.44	11.411%	$167.6067	$167.61	$167.60	$167.60
Purchase #4	$98.91	13.331%	$112.0957	$112.10	$112.10	$112.10
Purchase #5	$26.25	5.407%	$27.6693	$27.67	$27.65	$27.70
Purchase #6	$37.98	7.357%	$40.7742	$40.77	$40.75	$40.80
Purchase #7	$148.70	4.678%	$155.6562	$155.66	$155.65	$155.70
7 purchase totals =	$764.22		$824.8505	$824.86	$824.80	$824.90