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	$51.57	11.629%	$57.5671	$57.57	$57.55	$57.60
Purchase #2	$169.39	10.734%	$187.5723	$187.57	$187.55	$187.60
Purchase #3	$108.79	9.606%	$119.2404	$119.24	$119.25	$119.20
Purchase #4	$104.61	6.695%	$111.6136	$111.61	$111.60	$111.60
Purchase #5	$30.92	5.417%	$32.5949	$32.59	$32.60	$32.60
Purchase #6	$184.74	11.534%	$206.0479	$206.05	$206.05	$206.00
Purchase #7	$61.85	12.294%	$69.4538	$69.45	$69.45	$69.50
7 purchase totals =	$711.87		$784.0900	$784.08	$784.05	$784.10