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	$234.71	13.299%	$265.9241	$265.92	$265.90	$265.90
Purchase #2	$114.91	11.159%	$127.7328	$127.73	$127.75	$127.70
Purchase #3	$121.85	3.762%	$126.434	$126.43	$126.45	$126.40
Purchase #4	$114.95	4.785%	$120.4504	$120.45	$120.45	$120.50
Purchase #5	$89.36	11.814%	$99.917	$99.92	$99.90	$99.90
Purchase #6	$120.36	6.824%	$128.5734	$128.57	$128.55	$128.60
Purchase #7	$119.95	6.665%	$127.9447	$127.94	$127.95	$127.90
7 purchase totals =	$916.09		$996.9764	$996.96	$996.95	$996.90