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	$76.50	6.475%	$81.4534	$81.45	$81.45	$81.50
Purchase #2	$79.36	4.736%	$83.1185	$83.12	$83.10	$83.10
Purchase #3	$39.82	4.298%	$41.5315	$41.53	$41.55	$41.50
Purchase #4	$27.79	5.144%	$29.2195	$29.22	$29.20	$29.20
Purchase #5	$227.76	12.419%	$256.0455	$256.05	$256.05	$256.00
Purchase #6	$100.48	3.807%	$104.3053	$104.31	$104.30	$104.30
Purchase #7	$37.83	13.292%	$42.8584	$42.86	$42.85	$42.90
7 purchase totals =	$589.54		$638.5321	$638.54	$638.50	$638.50