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	$91.97	12.164%	$103.1572	$103.16	$103.15	$103.20
Purchase #2	$238.96	13.183%	$270.4621	$270.46	$270.45	$270.50
Purchase #3	$179.96	11.510%	$200.6734	$200.67	$200.65	$200.70
Purchase #4	$156.59	10.305%	$172.7266	$172.73	$172.75	$172.70
Purchase #5	$99.27	10.659%	$109.8512	$109.85	$109.85	$109.90
Purchase #6	$227.26	5.179%	$239.0298	$239.03	$239.05	$239.00
Purchase #7	$118.31	3.439%	$122.3787	$122.38	$122.40	$122.40
7 purchase totals =	$1,112.32		$1,218.2790	$1,218.28	$1,218.30	$1,218.40