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	$7.49	10.368%	$8.2666	$8.27	$8.25	$8.30
Purchase #2	$102.43	3.396%	$105.9085	$105.91	$105.90	$105.90
Purchase #3	$42.68	5.282%	$44.9344	$44.93	$44.95	$44.90
Purchase #4	$39.56	9.665%	$43.3835	$43.38	$43.40	$43.40
Purchase #5	$93.83	5.832%	$99.3022	$99.30	$99.30	$99.30
Purchase #6	$95.58	10.328%	$105.4515	$105.45	$105.45	$105.50
Purchase #7	$135.28	6.597%	$144.2044	$144.20	$144.20	$144.20
7 purchase totals =	$516.85		$551.4511	$551.44	$551.45	$551.50