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	$226.88	12.608%	$255.485	$255.49	$255.50	$255.50
Purchase #2	$51.31	11.348%	$57.1327	$57.13	$57.15	$57.10
Purchase #3	$170.99	7.740%	$184.2246	$184.22	$184.20	$184.20
Purchase #4	$203.86	12.423%	$229.1855	$229.19	$229.20	$229.20
Purchase #5	$134.91	5.311%	$142.0751	$142.08	$142.10	$142.10
Purchase #6	$105.34	3.504%	$109.0311	$109.03	$109.05	$109.00
Purchase #7	$70.35	11.686%	$78.5711	$78.57	$78.55	$78.60
7 purchase totals =	$963.64		$1,055.7051	$1,055.71	$1,055.75	$1,055.70