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	$86.70	4.300%	$90.4281	$90.43	$90.45	$90.40
Purchase #2	$125.25	11.524%	$139.6838	$139.68	$139.70	$139.70
Purchase #3	$127.39	12.442%	$143.2399	$143.24	$143.25	$143.20
Purchase #4	$79.72	13.288%	$90.3132	$90.31	$90.30	$90.30
Purchase #5	$90.44	10.755%	$100.1668	$100.17	$100.15	$100.20
Purchase #6	$78.28	12.179%	$87.8137	$87.81	$87.80	$87.80
Purchase #7	$51.73	7.705%	$55.7158	$55.72	$55.70	$55.70
7 purchase totals =	$639.51		$707.3613	$707.36	$707.35	$707.30