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	$56.77	4.346%	$59.2372	$59.24	$59.25	$59.20
Purchase #2	$64.34	12.775%	$72.5594	$72.56	$72.55	$72.60
Purchase #3	$78.73	4.181%	$82.0217	$82.02	$82.00	$82.00
Purchase #4	$93.84	4.423%	$97.9905	$97.99	$98.00	$98.00
Purchase #5	$145.38	10.107%	$160.0736	$160.07	$160.05	$160.10
Purchase #6	$131.53	5.777%	$139.1285	$139.13	$139.15	$139.10
Purchase #7	$21.59	7.735%	$23.26	$23.26	$23.25	$23.30
7 purchase totals =	$592.18		$634.2709	$634.27	$634.25	$634.30