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	$25.41	13.616%	$28.8698	$28.87	$28.85	$28.90
Purchase #2	$52.35	10.543%	$57.8693	$57.87	$57.85	$57.90
Purchase #3	$184.32	13.429%	$209.0723	$209.07	$209.05	$209.10
Purchase #4	$178.40	12.414%	$200.5466	$200.55	$200.55	$200.50
Purchase #5	$232.96	8.125%	$251.888	$251.89	$251.90	$251.90
Purchase #6	$33.79	8.180%	$36.554	$36.55	$36.55	$36.60
Purchase #7	$32.81	8.195%	$35.4988	$35.50	$35.50	$35.50
7 purchase totals =	$740.04		$820.2988	$820.30	$820.25	$820.40