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	$77.92	12.198%	$87.4247	$87.42	$87.40	$87.40
Purchase #2	$59.44	9.204%	$64.9109	$64.91	$64.90	$64.90
Purchase #3	$204.57	6.858%	$218.5994	$218.60	$218.60	$218.60
Purchase #4	$67.50	7.429%	$72.5146	$72.51	$72.50	$72.50
Purchase #5	$92.82	4.419%	$96.9217	$96.92	$96.90	$96.90
Purchase #6	$89.91	8.553%	$97.6	$97.60	$97.60	$97.60
Purchase #7	$139.73	7.745%	$150.5521	$150.55	$150.55	$150.60
7 purchase totals =	$731.89		$788.5234	$788.51	$788.45	$788.50