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	$249.42	12.506%	$280.6125	$280.61	$280.60	$280.60
Purchase #2	$56.78	8.645%	$61.6886	$61.69	$61.70	$61.70
Purchase #3	$68.72	6.524%	$73.2033	$73.20	$73.20	$73.20
Purchase #4	$243.73	11.302%	$271.2764	$271.28	$271.30	$271.30
Purchase #5	$54.62	12.783%	$61.6021	$61.60	$61.60	$61.60
Purchase #6	$142.71	13.693%	$162.2513	$162.25	$162.25	$162.30
Purchase #7	$220.25	11.535%	$245.6558	$245.66	$245.65	$245.70
7 purchase totals =	$1,036.23		$1,156.2900	$1,156.29	$1,156.30	$1,156.40