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	$37.74	5.589%	$39.8493	$39.85	$39.85	$39.80
Purchase #2	$216.83	11.393%	$241.5334	$241.53	$241.55	$241.50
Purchase #3	$188.53	12.294%	$211.7079	$211.71	$211.70	$211.70
Purchase #4	$213.66	5.395%	$225.187	$225.19	$225.20	$225.20
Purchase #5	$185.42	3.474%	$191.8615	$191.86	$191.85	$191.90
Purchase #6	$26.25	11.492%	$29.2667	$29.27	$29.25	$29.30
Purchase #7	$128.29	9.858%	$140.9368	$140.94	$140.95	$140.90
7 purchase totals =	$996.72		$1,080.3426	$1,080.35	$1,080.35	$1,080.30