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	$57.47	6.443%	$61.1728	$61.17	$61.15	$61.20
Purchase #2	$216.71	10.360%	$239.1612	$239.16	$239.15	$239.20
Purchase #3	$96.25	9.269%	$105.1714	$105.17	$105.15	$105.20
Purchase #4	$36.44	4.404%	$38.0448	$38.04	$38.05	$38.00
Purchase #5	$206.82	8.171%	$223.7193	$223.72	$223.70	$223.70
Purchase #6	$96.72	13.273%	$109.5576	$109.56	$109.55	$109.60
Purchase #7	$190.87	9.619%	$209.2298	$209.23	$209.25	$209.20
7 purchase totals =	$901.28		$986.0569	$986.05	$986.00	$986.10