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	$80.30	13.874%	$91.4408	$91.44	$91.45	$91.40
Purchase #2	$117.69	4.659%	$123.1732	$123.17	$123.15	$123.20
Purchase #3	$66.56	5.201%	$70.0218	$70.02	$70.00	$70.00
Purchase #4	$110.48	11.470%	$123.1521	$123.15	$123.15	$123.20
Purchase #5	$77.41	5.550%	$81.7063	$81.71	$81.70	$81.70
Purchase #6	$50.31	3.747%	$52.1951	$52.20	$52.20	$52.20
Purchase #7	$133.48	4.497%	$139.4826	$139.48	$139.50	$139.50
7 purchase totals =	$636.23		$681.1719	$681.17	$681.15	$681.20