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	$35.42	5.357%	$37.3174	$37.32	$37.30	$37.30
Purchase #2	$92.56	13.361%	$104.9269	$104.93	$104.95	$104.90
Purchase #3	$20.78	10.553%	$22.9729	$22.97	$22.95	$23.00
Purchase #4	$218.60	13.873%	$248.9264	$248.93	$248.95	$248.90
Purchase #5	$164.77	12.367%	$185.1471	$185.15	$185.15	$185.10
Purchase #6	$51.68	5.671%	$54.6108	$54.61	$54.60	$54.60
Purchase #7	$79.68	3.844%	$82.7429	$82.74	$82.75	$82.70
7 purchase totals =	$663.49		$736.6444	$736.65	$736.65	$736.50