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	$70.51	11.137%	$78.3627	$78.36	$78.35	$78.40
Purchase #2	$74.69	11.261%	$83.1008	$83.10	$83.10	$83.10
Purchase #3	$134.33	6.206%	$142.6665	$142.67	$142.65	$142.70
Purchase #4	$127.73	10.811%	$141.5389	$141.54	$141.55	$141.50
Purchase #5	$183.85	5.383%	$193.7466	$193.75	$193.75	$193.70
Purchase #6	$61.65	8.737%	$67.0364	$67.04	$67.05	$67.00
Purchase #7	$85.80	9.659%	$94.0874	$94.09	$94.10	$94.10
7 purchase totals =	$738.56		$800.5393	$800.55	$800.55	$800.50