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	$88.57	12.598%	$99.728	$99.73	$99.75	$99.70
Purchase #2	$201.64	13.817%	$229.5006	$229.50	$229.50	$229.50
Purchase #3	$214.28	13.359%	$242.9057	$242.91	$242.90	$242.90
Purchase #4	$44.59	4.611%	$46.646	$46.65	$46.65	$46.60
Purchase #5	$114.61	8.751%	$124.6395	$124.64	$124.65	$124.60
Purchase #6	$127.82	12.278%	$143.5137	$143.51	$143.50	$143.50
Purchase #7	$83.57	7.540%	$89.8712	$89.87	$89.85	$89.90
7 purchase totals =	$875.08		$976.8047	$976.81	$976.80	$976.70