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	$137.90	13.292%	$156.2297	$156.23	$156.25	$156.20
Purchase #2	$140.78	13.659%	$160.0091	$160.01	$160.00	$160.00
Purchase #3	$176.83	6.814%	$188.8792	$188.88	$188.90	$188.90
Purchase #4	$178.30	7.558%	$191.7759	$191.78	$191.80	$191.80
Purchase #5	$215.54	10.305%	$237.7514	$237.75	$237.75	$237.80
Purchase #6	$126.47	10.278%	$139.4686	$139.47	$139.45	$139.50
Purchase #7	$242.78	8.355%	$263.0643	$263.06	$263.05	$263.10
7 purchase totals =	$1,218.60		$1,337.1782	$1,337.18	$1,337.20	$1,337.30