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	$27.32	4.630%	$28.5849	$28.58	$28.60	$28.60
Purchase #2	$73.93	6.409%	$78.6682	$78.67	$78.65	$78.70
Purchase #3	$249.62	12.486%	$280.7876	$280.79	$280.80	$280.80
Purchase #4	$92.59	7.469%	$99.5055	$99.51	$99.50	$99.50
Purchase #5	$45.62	13.681%	$51.8613	$51.86	$51.85	$51.90
Purchase #6	$90.61	8.211%	$98.05	$98.05	$98.05	$98.10
Purchase #7	$103.42	5.435%	$109.0409	$109.04	$109.05	$109.00
7 purchase totals =	$683.11		$746.4984	$746.50	$746.50	$746.60