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	$10.33	11.322%	$11.4996	$11.50	$11.50	$11.50
Purchase #2	$168.84	8.850%	$183.7823	$183.78	$183.80	$183.80
Purchase #3	$167.31	9.286%	$182.8464	$182.85	$182.85	$182.80
Purchase #4	$129.70	7.799%	$139.8153	$139.82	$139.80	$139.80
Purchase #5	$138.66	9.473%	$151.7953	$151.80	$151.80	$151.80
Purchase #6	$71.42	9.594%	$78.272	$78.27	$78.25	$78.30
Purchase #7	$153.35	10.306%	$169.1543	$169.15	$169.15	$169.20
7 purchase totals =	$839.61		$917.1652	$917.17	$917.15	$917.20