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	$25.47	6.189%	$27.0463	$27.05	$27.05	$27.00
Purchase #2	$55.86	9.644%	$61.2471	$61.25	$61.25	$61.20
Purchase #3	$191.58	11.675%	$213.947	$213.95	$213.95	$213.90
Purchase #4	$167.42	13.498%	$190.0184	$190.02	$190.00	$190.00
Purchase #5	$111.35	4.791%	$116.6848	$116.68	$116.70	$116.70
Purchase #6	$237.97	3.141%	$245.4446	$245.44	$245.45	$245.40
Purchase #7	$142.41	4.382%	$148.6504	$148.65	$148.65	$148.70
7 purchase totals =	$932.06		$1,003.0386	$1,003.04	$1,003.05	$1,002.90