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	$78.87	13.456%	$89.4827	$89.48	$89.50	$89.50
Purchase #2	$49.73	4.159%	$51.7983	$51.80	$51.80	$51.80
Purchase #3	$148.90	13.573%	$169.1102	$169.11	$169.10	$169.10
Purchase #4	$17.35	4.128%	$18.0662	$18.07	$18.05	$18.10
Purchase #5	$199.27	8.432%	$216.0724	$216.07	$216.05	$216.10
Purchase #6	$201.94	11.127%	$224.4099	$224.41	$224.40	$224.40
Purchase #7	$94.50	5.608%	$99.7996	$99.80	$99.80	$99.80
7 purchase totals =	$790.56		$868.7393	$868.74	$868.70	$868.80