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	$243.61	9.660%	$267.1427	$267.14	$267.15	$267.10
Purchase #2	$125.88	11.620%	$140.5073	$140.51	$140.50	$140.50
Purchase #3	$22.58	3.442%	$23.3572	$23.36	$23.35	$23.40
Purchase #4	$86.68	4.698%	$90.7522	$90.75	$90.75	$90.80
Purchase #5	$196.60	11.587%	$219.38	$219.38	$219.40	$219.40
Purchase #6	$85.44	6.431%	$90.9346	$90.93	$90.95	$90.90
Purchase #7	$224.31	4.375%	$234.1236	$234.12	$234.10	$234.10
7 purchase totals =	$985.10		$1,066.1976	$1,066.19	$1,066.20	$1,066.20