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	$208.25	7.206%	$223.2565	$223.26	$223.25	$223.30
Purchase #2	$111.80	11.709%	$124.8907	$124.89	$124.90	$124.90
Purchase #3	$205.81	13.667%	$233.9381	$233.94	$233.95	$233.90
Purchase #4	$243.83	10.857%	$270.3026	$270.30	$270.30	$270.30
Purchase #5	$147.50	10.438%	$162.8961	$162.90	$162.90	$162.90
Purchase #6	$96.89	7.123%	$103.7915	$103.79	$103.80	$103.80
Purchase #7	$17.62	9.589%	$19.3096	$19.31	$19.30	$19.30
7 purchase totals =	$1,031.70		$1,138.3851	$1,138.39	$1,138.40	$1,138.40