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	$71.70	8.628%	$77.8863	$77.89	$77.90	$77.90
Purchase #2	$204.89	12.115%	$229.7124	$229.71	$229.70	$229.70
Purchase #3	$77.57	13.859%	$88.3204	$88.32	$88.30	$88.30
Purchase #4	$118.38	10.345%	$130.6264	$130.63	$130.65	$130.60
Purchase #5	$27.70	13.202%	$31.357	$31.36	$31.35	$31.40
Purchase #6	$40.35	12.580%	$45.426	$45.43	$45.45	$45.40
Purchase #7	$93.39	11.149%	$103.8021	$103.80	$103.80	$103.80
7 purchase totals =	$633.98		$707.1306	$707.14	$707.15	$707.10