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	$134.32	4.689%	$140.6183	$140.62	$140.60	$140.60
Purchase #2	$200.82	4.358%	$209.5717	$209.57	$209.55	$209.60
Purchase #3	$42.74	13.454%	$48.4902	$48.49	$48.50	$48.50
Purchase #4	$91.89	11.616%	$102.5639	$102.56	$102.55	$102.60
Purchase #5	$140.54	4.113%	$146.3204	$146.32	$146.30	$146.30
Purchase #6	$32.57	5.787%	$34.4548	$34.45	$34.45	$34.50
Purchase #7	$171.25	4.108%	$178.285	$178.29	$178.30	$178.30
7 purchase totals =	$814.13		$860.3043	$860.30	$860.25	$860.40