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	$170.49	10.735%	$188.7921	$188.79	$188.80	$188.80
Purchase #2	$204.64	4.201%	$213.2369	$213.24	$213.25	$213.20
Purchase #3	$43.95	4.365%	$45.8684	$45.87	$45.85	$45.90
Purchase #4	$127.80	5.225%	$134.4776	$134.48	$134.50	$134.50
Purchase #5	$93.37	8.578%	$101.3793	$101.38	$101.40	$101.40
Purchase #6	$133.71	4.593%	$139.8513	$139.85	$139.85	$139.90
Purchase #7	$56.92	4.796%	$59.6499	$59.65	$59.65	$59.60
7 purchase totals =	$830.88		$883.2555	$883.26	$883.30	$883.30