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	$128.77	8.308%	$139.4682	$139.47	$139.45	$139.50
Purchase #2	$197.75	8.851%	$215.2529	$215.25	$215.25	$215.30
Purchase #3	$51.86	4.748%	$54.3223	$54.32	$54.30	$54.30
Purchase #4	$67.43	6.727%	$71.966	$71.97	$71.95	$72.00
Purchase #5	$35.46	4.187%	$36.9447	$36.94	$36.95	$36.90
Purchase #6	$233.56	9.199%	$255.0452	$255.05	$255.05	$255.00
Purchase #7	$238.85	7.375%	$256.4652	$256.47	$256.45	$256.50
7 purchase totals =	$953.68		$1,029.4645	$1,029.47	$1,029.40	$1,029.50