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	$18.59	11.677%	$20.7608	$20.76	$20.75	$20.80
Purchase #2	$80.37	9.313%	$87.8549	$87.85	$87.85	$87.90
Purchase #3	$17.77	5.534%	$18.7534	$18.75	$18.75	$18.80
Purchase #4	$81.89	12.859%	$92.4202	$92.42	$92.40	$92.40
Purchase #5	$55.75	12.412%	$62.6697	$62.67	$62.65	$62.70
Purchase #6	$89.91	3.279%	$92.8581	$92.86	$92.85	$92.90
Purchase #7	$248.44	3.272%	$256.569	$256.57	$256.55	$256.60
7 purchase totals =	$592.72		$631.8861	$631.88	$631.80	$632.10