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	$16.25	9.336%	$17.7671	$17.77	$17.75	$17.80
Purchase #2	$64.72	9.477%	$70.8535	$70.85	$70.85	$70.90
Purchase #3	$175.25	13.508%	$198.9228	$198.92	$198.90	$198.90
Purchase #4	$162.57	4.464%	$169.8271	$169.83	$169.85	$169.80
Purchase #5	$39.49	7.770%	$42.5584	$42.56	$42.55	$42.60
Purchase #6	$65.53	8.574%	$71.1485	$71.15	$71.15	$71.10
Purchase #7	$69.59	4.693%	$72.8559	$72.86	$72.85	$72.90
7 purchase totals =	$593.40		$643.9333	$643.94	$643.90	$644.00