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	$125.31	13.712%	$142.4925	$142.49	$142.50	$142.50
Purchase #2	$144.42	8.457%	$156.6336	$156.63	$156.65	$156.60
Purchase #3	$44.77	12.735%	$50.4715	$50.47	$50.45	$50.50
Purchase #4	$187.75	12.310%	$210.862	$210.86	$210.85	$210.90
Purchase #5	$161.93	5.793%	$171.3106	$171.31	$171.30	$171.30
Purchase #6	$75.75	8.772%	$82.3948	$82.39	$82.40	$82.40
Purchase #7	$169.78	10.819%	$188.1485	$188.15	$188.15	$188.10
7 purchase totals =	$909.71		$1,002.3135	$1,002.30	$1,002.30	$1,002.30