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	$42.57	6.836%	$45.4801	$45.48	$45.50	$45.50
Purchase #2	$130.28	9.860%	$143.1256	$143.13	$143.15	$143.10
Purchase #3	$192.66	12.592%	$216.9197	$216.92	$216.90	$216.90
Purchase #4	$119.55	9.815%	$131.2838	$131.28	$131.30	$131.30
Purchase #5	$9.79	8.784%	$10.65	$10.65	$10.65	$10.70
Purchase #6	$196.48	10.348%	$216.8118	$216.81	$216.80	$216.80
Purchase #7	$169.49	7.649%	$182.4543	$182.45	$182.45	$182.50
7 purchase totals =	$860.82		$946.7253	$946.72	$946.75	$946.80