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	$34.66	8.838%	$37.7233	$37.72	$37.70	$37.70
Purchase #2	$158.44	8.469%	$171.8583	$171.86	$171.85	$171.90
Purchase #3	$40.62	9.773%	$44.5898	$44.59	$44.60	$44.60
Purchase #4	$101.48	11.280%	$112.9269	$112.93	$112.95	$112.90
Purchase #5	$171.26	10.634%	$189.4718	$189.47	$189.45	$189.50
Purchase #6	$162.46	11.178%	$180.6198	$180.62	$180.60	$180.60
Purchase #7	$31.30	12.521%	$35.2191	$35.22	$35.20	$35.20
7 purchase totals =	$700.22		$772.4090	$772.41	$772.35	$772.40