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	$177.85	3.654%	$184.3486	$184.35	$184.35	$184.30
Purchase #2	$32.91	7.126%	$35.2552	$35.26	$35.25	$35.30
Purchase #3	$74.47	6.714%	$79.4699	$79.47	$79.45	$79.50
Purchase #4	$137.67	3.495%	$142.4816	$142.48	$142.50	$142.50
Purchase #5	$102.95	10.600%	$113.8627	$113.86	$113.85	$113.90
Purchase #6	$148.97	13.107%	$168.4955	$168.50	$168.50	$168.50
Purchase #7	$111.73	3.179%	$115.2819	$115.28	$115.30	$115.30
7 purchase totals =	$786.55		$839.1954	$839.20	$839.20	$839.30