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	$115.26	4.410%	$120.343	$120.34	$120.35	$120.30
Purchase #2	$224.92	13.603%	$255.5159	$255.52	$255.50	$255.50
Purchase #3	$78.52	4.326%	$81.9168	$81.92	$81.90	$81.90
Purchase #4	$23.31	8.657%	$25.3279	$25.33	$25.35	$25.30
Purchase #5	$250.87	11.690%	$280.1967	$280.20	$280.20	$280.20
Purchase #6	$210.54	13.498%	$238.9587	$238.96	$238.95	$239.00
Purchase #7	$39.31	8.336%	$42.5869	$42.59	$42.60	$42.60
7 purchase totals =	$942.73		$1,044.8459	$1,044.86	$1,044.85	$1,044.80