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	$63.27	3.241%	$65.3206	$65.32	$65.30	$65.30
Purchase #2	$90.72	6.204%	$96.3483	$96.35	$96.35	$96.30
Purchase #3	$94.97	5.751%	$100.4317	$100.43	$100.45	$100.40
Purchase #4	$179.88	5.422%	$189.6331	$189.63	$189.65	$189.60
Purchase #5	$34.83	10.560%	$38.508	$38.51	$38.50	$38.50
Purchase #6	$216.99	12.162%	$243.3803	$243.38	$243.40	$243.40
Purchase #7	$243.60	5.746%	$257.5973	$257.60	$257.60	$257.60
7 purchase totals =	$924.26		$991.2193	$991.22	$991.25	$991.10