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	$145.83	7.210%	$156.3443	$156.34	$156.35	$156.30
Purchase #2	$115.71	10.172%	$127.48	$127.48	$127.50	$127.50
Purchase #3	$233.45	7.542%	$251.0568	$251.06	$251.05	$251.10
Purchase #4	$98.71	10.847%	$109.4171	$109.42	$109.40	$109.40
Purchase #5	$49.76	12.131%	$55.7964	$55.80	$55.80	$55.80
Purchase #6	$86.74	8.136%	$93.7972	$93.80	$93.80	$93.80
Purchase #7	$79.73	12.614%	$89.7871	$89.79	$89.80	$89.80
7 purchase totals =	$809.93		$883.6789	$883.69	$883.70	$883.70