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	$100.25	12.129%	$112.4093	$112.41	$112.40	$112.40
Purchase #2	$78.68	8.474%	$85.3473	$85.35	$85.35	$85.30
Purchase #3	$97.63	8.383%	$105.8143	$105.81	$105.80	$105.80
Purchase #4	$57.47	9.179%	$62.7452	$62.75	$62.75	$62.70
Purchase #5	$29.50	6.839%	$31.5175	$31.52	$31.50	$31.50
Purchase #6	$60.61	4.153%	$63.1271	$63.13	$63.15	$63.10
Purchase #7	$213.42	7.423%	$229.2622	$229.26	$229.25	$229.30
7 purchase totals =	$637.56		$690.2229	$690.23	$690.20	$690.10