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	$28.41	10.339%	$31.3473	$31.35	$31.35	$31.30
Purchase #2	$155.68	4.118%	$162.0909	$162.09	$162.10	$162.10
Purchase #3	$39.32	5.681%	$41.5538	$41.55	$41.55	$41.60
Purchase #4	$123.91	12.548%	$139.4582	$139.46	$139.45	$139.50
Purchase #5	$168.42	7.764%	$181.4961	$181.50	$181.50	$181.50
Purchase #6	$239.32	10.241%	$263.8288	$263.83	$263.85	$263.80
Purchase #7	$69.26	4.763%	$72.5589	$72.56	$72.55	$72.60
7 purchase totals =	$824.32		$892.3340	$892.34	$892.35	$892.40