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	$12.34	11.851%	$13.8024	$13.80	$13.80	$13.80
Purchase #2	$164.30	5.184%	$172.8173	$172.82	$172.80	$172.80
Purchase #3	$190.34	9.844%	$209.0771	$209.08	$209.10	$209.10
Purchase #4	$43.89	6.649%	$46.8082	$46.81	$46.80	$46.80
Purchase #5	$92.84	13.425%	$105.3038	$105.30	$105.30	$105.30
Purchase #6	$166.86	7.116%	$178.7338	$178.73	$178.75	$178.70
Purchase #7	$166.59	13.107%	$188.425	$188.43	$188.45	$188.40
7 purchase totals =	$837.16		$914.9676	$914.97	$915.00	$914.90