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	$10.40	12.334%	$11.6827	$11.68	$11.70	$11.70
Purchase #2	$55.40	13.533%	$62.8973	$62.90	$62.90	$62.90
Purchase #3	$239.76	6.498%	$255.3396	$255.34	$255.35	$255.30
Purchase #4	$31.92	3.609%	$33.072	$33.07	$33.05	$33.10
Purchase #5	$231.45	12.775%	$261.0177	$261.02	$261.00	$261.00
Purchase #6	$40.33	13.472%	$45.7633	$45.76	$45.75	$45.80
Purchase #7	$83.96	13.295%	$95.1225	$95.12	$95.10	$95.10
7 purchase totals =	$693.22		$764.8951	$764.89	$764.85	$764.90