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	$229.89	12.356%	$258.2952	$258.30	$258.30	$258.30
Purchase #2	$169.56	5.511%	$178.9045	$178.90	$178.90	$178.90
Purchase #3	$219.28	5.449%	$231.2286	$231.23	$231.25	$231.20
Purchase #4	$166.91	8.802%	$181.6014	$181.60	$181.60	$181.60
Purchase #5	$97.86	8.602%	$106.2779	$106.28	$106.30	$106.30
Purchase #6	$17.60	7.337%	$18.8913	$18.89	$18.90	$18.90
Purchase #7	$88.34	4.453%	$92.2738	$92.27	$92.25	$92.30
7 purchase totals =	$989.44		$1,067.4727	$1,067.47	$1,067.50	$1,067.50