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	$85.34	5.173%	$89.7546	$89.75	$89.75	$89.80
Purchase #2	$222.69	7.540%	$239.4808	$239.48	$239.50	$239.50
Purchase #3	$96.89	8.190%	$104.8253	$104.83	$104.85	$104.80
Purchase #4	$169.65	10.186%	$186.9305	$186.93	$186.95	$186.90
Purchase #5	$215.93	4.574%	$225.8066	$225.81	$225.80	$225.80
Purchase #6	$130.81	6.691%	$139.5625	$139.56	$139.55	$139.60
Purchase #7	$22.72	13.782%	$25.8513	$25.85	$25.85	$25.90
7 purchase totals =	$944.03		$1,012.2116	$1,012.21	$1,012.25	$1,012.30