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	$92.74	13.714%	$105.4584	$105.46	$105.45	$105.50
Purchase #2	$66.54	8.157%	$71.9677	$71.97	$71.95	$72.00
Purchase #3	$119.80	6.660%	$127.7787	$127.78	$127.80	$127.80
Purchase #4	$182.67	3.451%	$188.9739	$188.97	$188.95	$189.00
Purchase #5	$128.89	7.302%	$138.3015	$138.30	$138.30	$138.30
Purchase #6	$94.73	3.748%	$98.2805	$98.28	$98.30	$98.30
Purchase #7	$42.98	5.516%	$45.3508	$45.35	$45.35	$45.40
7 purchase totals =	$728.35		$776.1115	$776.11	$776.10	$776.30