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	$5.42	10.689%	$5.9993	$6.00	$6.00	$6.00
Purchase #2	$152.40	7.655%	$164.0662	$164.07	$164.05	$164.10
Purchase #3	$92.31	6.686%	$98.4818	$98.48	$98.50	$98.50
Purchase #4	$114.26	4.770%	$119.7102	$119.71	$119.70	$119.70
Purchase #5	$70.58	11.670%	$78.8167	$78.82	$78.80	$78.80
Purchase #6	$149.73	3.645%	$155.1877	$155.19	$155.20	$155.20
Purchase #7	$144.48	4.423%	$150.8704	$150.87	$150.85	$150.90
7 purchase totals =	$729.18		$773.1323	$773.14	$773.10	$773.20