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	$104.25	3.715%	$108.1229	$108.12	$108.10	$108.10
Purchase #2	$109.86	5.672%	$116.0913	$116.09	$116.10	$116.10
Purchase #3	$79.80	12.243%	$89.5699	$89.57	$89.55	$89.60
Purchase #4	$99.67	13.207%	$112.8334	$112.83	$112.85	$112.80
Purchase #5	$237.54	5.320%	$250.1771	$250.18	$250.20	$250.20
Purchase #6	$19.63	11.211%	$21.8307	$21.83	$21.85	$21.80
Purchase #7	$172.74	12.117%	$193.6709	$193.67	$193.65	$193.70
7 purchase totals =	$823.49		$892.2962	$892.29	$892.30	$892.30