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	$128.72	12.258%	$144.4985	$144.50	$144.50	$144.50
Purchase #2	$16.83	11.163%	$18.7087	$18.71	$18.70	$18.70
Purchase #3	$25.72	13.812%	$29.2724	$29.27	$29.25	$29.30
Purchase #4	$73.96	12.331%	$83.08	$83.08	$83.10	$83.10
Purchase #5	$102.69	3.109%	$105.8826	$105.88	$105.90	$105.90
Purchase #6	$78.64	3.185%	$81.1447	$81.14	$81.15	$81.10
Purchase #7	$115.69	6.127%	$122.7783	$122.78	$122.80	$122.80
7 purchase totals =	$542.25		$585.3652	$585.36	$585.40	$585.40